Method for forming thermally conductive thermal radical cure silicone compositions

ABSTRACT

A method for forming a thermally conductive thermal radical cure silicone composition comprising (I) a clustered functional polyorganopolysiloxane; optionally (II) a silicone reactive diluent, (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator is provided. In this method, the clustered functional polyorganosiloxane (I) and the optional silicone reactive diluent (II) are premade prior to their addition to respective components (III), (III′) and (IV).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage filing under 35 U.S.C. § 371 of PCT Application No. PCT/US14/15578 filed on 10 Feb. 2014, which claims the benefit of U.S. Provisional Patent Application No. 61/763,141 filed 11 Feb. 2013 under 35 U.S.C. § 119 (e). PCT Application No. PCT/US14/15578 and U.S. Provisional Patent Application No. 61/763,141 are hereby incorporated by reference.

The present invention relates generally to methods for forming silicone compositions, and more specifically to methods for forming thermally conductive thermal radical cure silicone compositions.

Polyorganosiloxane compositions that cure to elastomeric materials are well known. Such compositions may be prepared by mixing polydiorganosiloxanes having curable (e.g., hydrolyzable, radiation curable, or heat curable) groups with crosslinking agents and/or catalysts, as needed. Generally, the polydiorganosiloxanes may have 1 to 3 reactive groups per chain end. Compositions including these components can then be cured, for example, by exposure to atmospheric moisture, exposure to radiation, or exposure to heat, depending on the curable groups present.

The cure rate of a particular composition depends on various factors including the type and number reactive group(s) present. It is known that different groups have different reactivities. For example, in the presence of moisture, a silicon-bonded acetoxy group will usually hydrolyze more rapidly than a silicon-bonded alkoxy group when all other conditions are the same. Furthermore, even the same type of curable group can have different reactivities depending on the number of those curable groups bonded to a particular silicon atom. For example, if a polydiorganosiloxane has three silicon-bonded alkoxy groups bonded to one silicon atom on a chain end, then the first alkoxy group is generally most reactive (reacts most quickly), but after the first alkoxy group reacts, it takes a longer time for the second alkoxy group bonded to the same silicon atom to react, and even longer for the third. Therefore, there is a continuing need to prepare clustered functional polyorganosiloxanes having more of the “most” reactive groups per molecular terminus.

Furthermore, to show utility for certain applications, such as silicone adhesive applications, a filler may be added to the composition to improve the physical property profile (e.g., increase tensile strength and increase % elongation to break) of the resulting cured product of the composition. The nature of the filler, its chemistry, particle size and surface chemistry have all been shown to influence the magnitude of the interaction between polyorganosiloxanes and the filler and consequently the ultimate physical properties. Other properties such as adhesion and dispensability also play a role in the performance and commercial acceptance of a composition for adhesive applications. Silicone adhesives generally have tensile properties in excess of 200 pounds per square inch (psi) and 100% elongation, with adhesion to a wide variety of metal, mineral and plastic surfaces.

The synthesis of ‘dumb-bell’ silicone polymers, in which long polymer chains are capped with cyclic, linear and star-shaped species having one or more organo-functional groups has been disclosed. Such polymers have been described which can undergo a number of cure chemistries, e.g., epoxy (glycidyl, alkylepoxy, and cycloaliphatic epoxy), methacrylate, acrylate, urethanes, alkoxy, or addition.

It is desirable to make multifunctional end blocked polymers (clustered functional polyorganosiloxanes) in which the curable groups are clustered at the ends/termini of the polymers. The combination of clustered functional groups with nonfunctional polymer chains separating them in the ‘dumb-bell’ silicone polymers may provide higher physical properties with the minimum drop in cure rate. This approach has been demonstrated for ‘dumb-bell’ silicone polymers in which the curable groups are the same (for example, all curable groups clustered at the polymer chain ends may be either epoxy or alkoxy). This approach has also been demonstrated for so called ‘multiple cure’ systems in which the curable groups differ, for example, all curable groups clustered at the polymer terminals may be a combination of epoxy and alkoxy groups.

Thermally conductive silicone compositions including these clustered functional polyorganosiloxanes are utilized in bonding hybrid circuit substrates, power semiconductor components and devices to heat sinks as well as for use in other bonding applications where flexibility and thermal conductivity are major concerns. The low viscosity versions of these thermally conductive silicone compositions are ideal for use as thermally conductive potting materials for transformers, power supplies, coils and other electronic devices that require improved thermal dissipation.

In order to make these curable polyorganosiloxane compositions more dispensable for application purposes, it is often necessary or desirable to reduce their viscosities through the use of viscosity reducing polymers, sometimes referred to as reactive diluents. Such reactive diluents should be compatible with the curable polyorganosiloxane compositions and function to reduce viscosity without adversely affecting properties of the composition both prior to application (such as storage stability) and subsequent to application (including curing rates and cured physical properties of the compositions).

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a method, hereinafter referred to as a Premade Polymer Method, for forming a thermally conductive thermal radical cure silicone composition comprising (I) a clustered functional polyorganopolysiloxane; (II) a silicone reactive diluent; (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator, the method comprising:

(A) providing a clustered functional polyorganosiloxane (I) that comprises the reaction product of a reaction of:

-   -   a) a polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups,     -   b) a polyorganohydrogensiloxane having an average, per molecule,         of 4 to 15 silicon atoms and at least 4 silicon bonded hydrogen         atoms per aliphatically unsaturated organic group in component         a),     -   c) a reactive species having, per molecule at least one         aliphatically unsaturated organic group and one or more curable         groups selected from acrylate groups and methacrylate groups,         and     -   in the presence of d) a hydrosilylation catalyst and e) an         isomer reducing agent,

(B) forming a mixture by mixing the filler (III) comprising the thermally conductive filler, the filler treating agent (III′), and at least one of the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I);

(C) heating the mixture to a temperature from 50° C. to 110° C. to in situ treat thermally conductive filler with the filler treating agent (III′) in the presence of the at least one of the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I);

(D) introducing either the silicone reactive diluent (II) or the clustered functional polyorganosiloxane (I) to the mixture such that the mixture includes both the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I) when the mixture of Step (B) does not include both the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I); and then

(E) cooling the mixture to 30° C. or less and blending a radical initiator (IV) with the mixture.

In an alternative method, the thermally conductive thermal radical cure silicone composition can be made in a modified Premade Polymer process that does not include the silicone reactive diluent. In this alternative method, thermally conductive thermal radical cure silicone composition comprises (I) a clustered functional polyorganopolysiloxane; (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator and is formed by the method comprising:

(A) providing a clustered functional polyorganosiloxane (I) that comprises the reaction product of a reaction of:

-   -   a) a polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups,     -   b) a polyorganohydrogensiloxane having an average, per molecule,         of 4 to 15 silicon atoms and at least 4 silicon bonded hydrogen         atoms per aliphatically unsaturated organic group in component         a),     -   c) a reactive species having, per molecule at least one         aliphatically unsaturated organic group and one or more curable         groups selected from acrylate groups and methacrylate groups,         and     -   in the presence of d) a hydrosilylation catalyst and e) an         isomer reducing agent,

(B) forming a mixture by mixing the filler (III) comprising the thermally conductive filler, the filler treating agent (III′), and the clustered functional polyorganosiloxane (I);

(C) heating the mixture to a temperature from 50° C. to 110° C. to in situ treat thermally conductive filler with the filler treating agent (III′) in the presence of the clustered functional polyorganosiloxane (I); and then

(D) cooling the mixture to 30° C. or less and blending a radical initiator (IV) with the mixture.

This thermally conductive silicone composition formed by the Premade Polymer Method according to either alternative method offers many advantages over prior thermally conductive silicone compositions due to its ability to cure by two distinct methods, namely moisture cure and thermal radical cure, without adversely affecting its mechanical and physical properties. Thus, the silicone composition may be used over a wider variety of substrates, including plastic substrates and metal substrates. Moreover, the Premade Polymer method allows for the use of less pure forms of the fillers (III) into the resultant compositions than previously realized.

Thermally conductive thermal radical cure silicone compositions formed by the Premade Polymer Method are useful in composite articles of manufacture in which substrates are coated or bonded together with thermally conductive thermal radical cure silicone composition and cured. They can also be used in the preparation of various electrically conductive rubbers, electrically conductive tapes, electrically conductive adhesives, electrically conductive foams, and electrically conductive pressure sensitive adhesives; especially where the rubber, tape, adhesive, or pressure sensitive adhesive, are electrically conductive silicone rubbers, electrically conductive silicone tapes, electrically conductive silicone adhesives, electrically conductive silicone foams, and electrically conductive silicone pressure sensitive adhesives.

Thermally conductive thermal radical cure silicone composition formed by the Premade Polymer Method are useful in composite articles of manufacture in which substrates are coated or bonded together with thermally conductive thermal radical cure silicone composition and cured. Thermally conductive thermal radical cure silicone composition can also be used to prepare thermal interface materials, thermally conductive rubbers, thermally conductive tapes, thermally conductive curable adhesives, thermally conductive foams, and thermally conductive pressure sensitive adhesives. They are especially useful for preparing thermally conductive thermal radical cure silicone compositions used as die attachment adhesives, solder replacements, and thermally conductive coatings and gaskets. Thermally conductive thermal radical cure silicone compositions are especially useful for bonding electronic components to flexible or rigid substrates

These and other features of the invention will become apparent from a consideration of the description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The articles ‘a’, ‘an’, and ‘the’ each refer to one or more, unless otherwise indicated. All amounts, ratios, and percentages in this application are by weight, unless otherwise indicated. All kinematic viscosities were measured at 25° C., unless otherwise indicated.

The present invention relates to a novel method, hereinafter referred to as the “Premade Polymer Route”, for forming a thermally conductive thermal radical cure silicone composition comprising (I) a clustered functional polyorganopolysiloxane; optionally (II) a silicone reactive diluent (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator, as well as other optional components.

In the Premade Polymer Route, the clustered functional polyorganosiloxane (I) and the silicone reactive diluents (II) are premade prior to their addition to components (III), (III′) and (IV) and the other optional components.

As will be discussed further below, the Premade Polymer Route offers unique advantages for producing thermally conductive thermal radical cure silicone compositions having higher and lower viscosities due to its ability to cure by two distinct methods, namely moisture cure and thermal radical cure, without adversely affecting its mechanical and physical properties. Thus, the composition may be used over a wider variety of substrates, including plastic substrates and metal substrates. Moreover, the Premade Polymer method allows for the use of less pure forms of the fillers (III) into the resultant compositions than previously realized.

Component (I) is a clustered functional polyorganopolysiloxane comprises the reaction product of a reaction of:

-   -   a) a polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups;     -   b) a polyorganohydrogensiloxane having an average of 4 to 15         silicon atoms per molecule; and     -   c) a reactive species having, per molecule, at least 1         aliphatically unsaturated organic group and 1 or more curable         groups;     -   in the presence of d) a hydrosilylation catalyst; and e) an         isomer reducing agent; and     -   optional additional components.

A weight percent of silicon bonded hydrogen atoms in component b) divided by a weight percent aliphatically unsaturated organic groups in component a) (the SiH_(b)/Vi_(a) ratio) ranges from 4/1 to 20/1.

In certain embodiments, the process for forming the clustered functional polyorganopolysiloxane (I) in a first embodiment may comprise:

1) concurrently reacting components comprising

-   -   a) a polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups,     -   b) a polyorganohydrogensiloxane having an average, per molecule,         of 4 to 15 Si atoms and at least 4 silicon bonded hydrogen atoms         per aliphatically unsaturated organic group in component a), and     -   c) a reactive species having, per molecule, at least 1         aliphatically unsaturated organic group and 1 or more radical         curable groups selected from acrylate groups and methacrylate         groups;

in the presence of d) a hydrosilylation catalyst and e) an isomer reducing agent.

In this process, the components in step 1) may further comprise f) a filler, g) a non-reactive silicone resin, or a combination thereof. The processes described above may optionally further comprise the steps of: 2) adding a catalyst inhibitor to deactivate the catalyst after step 1), and 3) purifying the product of step 2).

Alternatively, the process for forming the clustered functional polyorganopolysiloxane in a second embodiment (I) may comprise:

A) concurrently reacting components comprising

-   -   a) the polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups; and     -   b) the polyorganohydrogensiloxane having an average, per         molecule, of 4 to 15 Si atoms and at least 4 silicon bonded         hydrogen atoms per aliphatically unsaturated organic group in         component a),     -   in the presence of d) the hydrosilylation catalyst; and         thereafter

B) reacting the product of step A) with an component comprising:

-   -   c) the reactive species having, per molecule, at least 1         aliphatically unsaturated organic group and one or more radical         curable groups selected from acrylate groups and methacrylate         groups;     -   in the presence of e) an isomer reducing agent;     -   with the proviso that the components in step A) and/or step B)         further comprise f) a filler, g) a non-reactive silicone resin,         or a combination thereof; and with the proviso that no         intermediate purification step is performed between step A) and         step B), and with the proviso that the SiH_(b)/Vi_(a) ratio         ranges from 4/1 to 20/1, and a product prepared by the process         has, on average, more than one curable group at each terminus of         the polyorganosiloxane of component a).

The process may optionally further comprise the steps of: C) adding a catalyst inhibitor to deactivate the catalyst after step B), and D) purifying the product of step C). The step of purifying the products in the above processes may be performed by any convenient means, such as stripping or distillation, optionally under vacuum.

In certain embodiments, the clustered functional organopolysiloxane (I) comprises from 20 to 99.9 weight percent, such as from 30 to 60 weight percent, of the total silicone matrix weight of the curable silicone composition (i.e., the total combined weight of the clustered functional organopolysiloxane (I) and silicone reactive diluent (II)).

Component a) is a polyorganosiloxane having an average, per molecule, of at least 2 aliphatically unsaturated organic groups, which are capable of undergoing a hydrosilylation reaction with a silicon bonded hydrogen atom of component b). Component a) may have a linear or branched structure. Alternatively, component a) may have a linear structure. Component a) may be a combination comprising two or more polyorganosiloxanes that differ in at least one of the following properties: structure, viscosity, degree of polymerization, and sequence.

Component a) has a minimum average degree of polymerization (average DP) of 100. Alternatively, average DP of component a) may range from 100 to 1000. The distribution DP of polyorganosiloxanes of component a) can be bimodal. For example, component a) may comprise one alkenyl terminated polydiorganosiloxane with a DP of 60 and another alkenyl terminated polydiorganosiloxane with a DP higher than 100, provided that average DP of the polydiorganosiloxanes ranges from 100 to 1000. However, suitable polyorganosiloxanes for use in component a) have a minimum degree of polymerization (DP) of 10, provided that polyorganosiloxanes with DP less than 10 are combined with polyorganosiloxanes having DP greater than 100. Suitable polydiorganosiloxanes for component a) are known in the art and are commercially available. For example, DOW CORNING® SFD-128 has DP ranging from 800 to 1000, DOW CORNING® SFD-120 has DP ranging from 600 to 700, DOW® CORNING® 7038 has DP of 100, DOW CORNING® SFD-119 has DP of 150. All of these are vinyl-terminated polydimethylsiloxanes are commercially available from Dow Corning® Corporation of Midland, Mich., USA. When component a) has a bimodal distribution, the polyorganosiloxane with the lower DP (low DP polyorganosiloxane) is present in a lower amount than the polyorganosiloxane with the higher DP (high DP polyorganosiloxane). For example, in a bimodal distribution, the ratio of low DP polyorganosiloxane/high DP polyorganosiloxane may range from 10/90 to 25/75.

Component a) is exemplified by polyorganosiloxanes of formula (I), formula (II), or a combination thereof. Formula (I) is R⁷ ₂R⁸SiO(R¹ ₂SiO)_(g)(R⁷R⁸SiO)_(h)SiR⁷ ₂R⁸, and formula (II) is R⁷ ₃SiO(R⁷ ₂SiO)_(i)(R⁷R⁸SiO)_(j)SiR⁷ ₃. In these formulae, each R⁷ is independently a monovalent organic group free of aliphatic unsaturation, each R⁸ is independently an aliphatically unsaturated organic group, subscript g has an average value ranging from 2 to 1000, subscript h has an average value ranging from 0 to 1000, subscript i has an average value ranging from 0 to 1000, and subscript j has an average value ranging from 4 to 1000. In formulae (I) and (II), 10≤(g+h)≤1000 and 10≤(i+j)≤1000.

Suitable monovalent organic groups for R⁷ include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl. Each R⁸ is independently an aliphatically unsaturated monovalent organic group. R⁸ may be an aliphatically unsaturated monovalent hydrocarbon group exemplified by alkenyl groups such as vinyl, allyl, propenyl, and butenyl; and alkynyl groups such as ethynyl and propynyl.

Component a) may comprise a polydiorganosiloxane such as i) dimethylvinylsiloxy-terminated polydimethylsiloxane, ii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane), iii) dimethylvinylsiloxy-terminated polymethylvinylsiloxane, iv) trimethylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane), v) trimethylsiloxy-terminated polymethylvinylsiloxane, vi) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylphenylsiloxane), vii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/diphenylsiloxane), viii) phenyl, methyl, vinyl-siloxy-terminated polydimethylsiloxane, ix) dimethylhexenylsiloxy-terminated polydimethylsiloxane, x) dimethylhexenylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), xi) dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane, xii) trimethylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), or xiii) a combination thereof.

Component b) is a polyorganohydrogensiloxane having an average of 4 to 15 silicon atoms per molecule. Component b) has an average of at least 4 silicon bonded hydrogen atoms per aliphatically unsaturated organic group in component a). Component b) may be cyclic, branched, or linear. Alternatively, component b) may be cyclic. Component b) may be a combination comprising two or more polyorganohydrogensiloxanes that differ in at least one of the following properties: structure, viscosity, degree of polymerization, and sequence.

Component b) may be a cyclic polyorganohydrogensiloxane having an average of 4 to 15 siloxane units per molecule. The cyclic polyorganohydrogensiloxane may have formula (III), where formula (III) is (R⁹ ₂SiO_(2/2))_(k)(HR⁹SiO_(2/2))_(l), in which each R⁹ is independently a monovalent organic group free of aliphatic unsaturation, subscript k has an average value ranging from 0 to 10, subscript 1 has an average value ranging from 4 to 15, and a quantity (k+l) has a value ranging from 4 to 15, alternatively 4 to 12, alternatively 4 to 10, alternatively 4 to 6, and alternatively 5 to 6. Monovalent organic groups suitable for R⁹ include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Alternatively, component b) may be a branched polyorganohydrogensiloxane. The branched polyorganohydrogensiloxane for component b) may have formula (IV), where formula (IV) is Si—(OSiR¹⁰ ₂)_(m)(OSiHR¹⁰)_(m′)(OSiR¹⁰ ₃)_(n)(OSiR¹⁰ ₂H)_((4-n)), in which each R¹⁰ is independently a monovalent organic group free of aliphatic unsaturation, subscript m has a value ranging from 0 to 10, subscript m′ has a value ranging from 0 to 10, and subscript n has a value ranging from 0 to 1.

Alternatively, subscript m may be 0. When subscript m′ is 0, then subscript n is also 0. Monovalent organic groups suitable for R¹⁰ include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Alternatively, component b) may be a linear polyorganohydrogensiloxane having an average of at least 4 silicon bonded hydrogen atoms per molecule. The linear polyorganohydrogensiloxane for component b) may have a formula selected from (V), (VI), or a combination thereof, where formula (V) is R¹¹ ₂HSiO(R¹¹ ₂SiO)_(o)(R¹¹HSiO)_(p)SiR¹¹ ₂H, formula (VI) is R¹¹ ₃SiO(R¹¹ ₂SiO)_(q)(R¹¹HSiO)_(r)SiR¹¹ ₃; where each R¹¹ is independently a monovalent organic group free of aliphatic unsaturation, subscript o has an average value ranging from 0 to 12, subscript p has an average value ranging from 2 to 12, subscript q has an average value ranging from 0 to 12, and subscript r has an average value ranging from 4 to 12 where 4≤(o+p)≤13 and 4≤(q+r)≤13. Monovalent organic groups suitable for R¹¹ include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Component a) and component b) may be present in amounts sufficient to provide a weight percent of silicon bonded hydrogen atoms in component b)/weight percent of unsaturated organic groups in component a) (commonly referred to as SiH_(b)/Vi_(a) ratio) ranging from 4/1 to 20/1, alternatively 4/1 to 10/1, and alternatively 5/1 to 20/1. Without wishing to be bound by theory, it is thought that if SiH_(b)/Vi_(a) ratio is 30/1 or higher, the components may crosslink to form a product with undesirable physical properties; and if SiH_(b)/Vi_(a) ratio is less than 4/1, the product of the process may not have sufficient clustered functional groups to have fast enough cure speed, particularly if a monofunctional reactive species (having one curable group per molecule) is used as component c).

Without wishing to be bound by theory, it is thought that using an excess of silicon bonded hydrogen atoms in component b), relative to aliphatically unsaturated organic groups in component a), may reduce the possibilities of producing high homologs of the clustered functional polyorganosiloxanes, which tend to be insoluble in, and may reduce storage life of, a curable silicone composition containing the clustered functional polyorganosiloxane prepared by the process described herein. The excess of silicon bonded hydrogen atoms in component b) may also result in small (relatively low DP) clustered functional polyorganosiloxanes, which may act as reactive diluents or viscosity modifiers and adhesion promoters. It is difficult to make these highly functional small molecules in an industrial environment because the inhibiting nature of small highly functional silicone hydrides means temperatures above 50° C. are typically required to initiate the hydrosilylation process. This is then followed by a large exotherm, which can be dangerous in the presence of large volumes of solvent, or if careful monitoring of reagents is not used to control the temperature. By simply changing the SiH_(b)/Vi_(a) ratio, these species can be made in a dilute solution of clustered functional polyorganosiloxane and filler, thereby significantly reducing gelation and chance of fire due to uncontrolled exothermic reaction.

Component c) is a reactive species. The reactive species may be any species that can provide the curable groups in the clustered functional polyorganosiloxane. The reactive species has an average, per molecule, of at least one aliphatically unsaturated organic group that is capable of undergoing an addition reaction with a silicon bonded hydrogen atom of component b). Component c) further comprises one or more radical curable groups per molecule. The radical curable groups are functional (reactive) groups that render the clustered functional polyorganosiloxane (prepared by the process described above) radiation curable. The radical curable groups on component c) may be selected from acrylate groups and methacrylate groups and combinations thereof. Alternatively, the curable groups on component c) may be selected from acrylate, alkoxy, epoxy, methacrylate, and combinations thereof.

For example, component c) may comprise a silane of formula (VIII), where formula (VIII) is R¹² _(s)SiR¹³ _((3-s)); in which subscript s has a value ranging from 1 to 3, each R¹² is independently an aliphatically unsaturated organic group, and each R¹³ is independently selected from an organic group containing an acrylate group and a methacrylate group.

Alternatively, component c) may comprise an organic compound (which does not contain a silicon atom). The organic compound for component c) may have an average, per molecule, of 1 to 2 aliphatically unsaturated organic groups, such as alkenyl or alkynyl groups, and one or more reactive groups selected from an acrylate group and a methacrylate group. Examples of suitable organic compounds for component c) include, but are not limited to, an allyl acrylate and allyl methacrylate (AMA); and combinations thereof.

The amount of component c) depends on various factors including the type, amount, and SiH content of component b) and the type of component c) selected. However, the amount of component c) is sufficient to make SiH_(tot)/Vi_(tot) range from 1/1 to 1/1.4, alternatively 1/1.2 to 1.1/1. The ratio SiH_(tot)/Vi_(tot) means the weight percent of silicon bonded hydrogen atoms on component b) and, if present component g) the chain extender and/or component h) the endcapper (described below), divided by the weight percent of aliphatically unsaturated organic groups on components a) and c) combined.

Component d) is a hydrosilylation catalyst which accelerates the reaction of components a), b), and c). Component d) may be added in an amount sufficient to promote the reaction of components a), b), and c), and this amount may be, for example, sufficient to provide 0.1 parts per million (ppm) to 1000 ppm of platinum group metal, alternatively 1 ppm to 500 ppm, alternatively 2 ppm to 200, alternatively 5 ppm to 150 ppm, based on the combined weight of all components used in the process.

Suitable hydrosilylation catalysts are known in the art and commercially available. Component d) may comprise a platinum group metal selected from platinum (Pt), rhodium, ruthenium, palladium, osmium or iridium metal or organometallic compound thereof, or a combination thereof. Component d) is exemplified by compounds such as chloroplatinic acid, chloroplatinic acid hexahydrate, platinum dichloride, and complexes of said compounds with low molecular weight organopolysiloxanes or platinum compounds microencapsulated in a matrix or coreshell type structure. Complexes of platinum with low molecular weight organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. These complexes may be microencapsulated in a resin matrix. Alternatively, the catalyst may comprise 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum. When the catalyst is a platinum complex with a low molecular weight organopolysiloxane, the amount of catalyst may range from 0.04% to 0.4% based on the combined weight of the components used in the process.

Suitable hydrosilylation catalysts for component d) are described in, for example, U.S. Pat. Nos. 3,159,601; 3,220,972; 3,296,291; 3,419,593; 3,516,946; 3,814,730; 3,989,668; 4,784,879; 5,036,117; and 5,175,325 and EP 0 347 895 B. Microencapsulated hydrosilylation catalysts and methods of preparing them are known in the art, as exemplified in U.S. Pat. Nos. 4,766,176; and 5,017,654.

Component e) is an isomer reducing agent. In certain embodiments, the isomer reducing agent comprises a carboxylic acid compound. The carboxylic acid compound may comprise (1) carboxylic acid, (2) an anhydride of a carboxylic acid, (3) a carboxylic silyl ester, and/or (4) a substance that will produce the above-mentioned carboxylic acid compounds (i.e., (1), (2), and/or (3)) through a reaction or decomposition in the reaction of the method. It is to be appreciated that a mixture of one or more of these carboxylic acid compounds may be utilized as the isomer reducing agent. For example, a carboxylic silyl ester may be utilized in combination with an anhydride of a carboxylic acid as the isomer reducing agent. In addition, a mixture within one or more types of carboxylic acid compounds may be utilized as the isomer reducing agent. For example, two different carboxylic silyl esters may be utilized in concert, or two carboxylic silyl esters may be utilized in concert with an anhydride of a carboxylic acid.

When the isomer reducing agent comprises (1) carboxylic acid, any carboxylic acid having carboxyl groups may be utilized. Suitable examples of carboxylic acids include saturated carboxylic acids, unsaturated carboxylic acids, monocarboxylic acids, and dicarboxylic acids. A saturated or unsaturated aliphatic hydrocarbon group, aromatic hydrocarbon group, halogenated hydrocarbon group, hydrogen atom, or the like is usually selected as the portion other than the carboxyl groups in these carboxylic acids. Specific examples of suitable carboxylic acids include saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, hexanoic acid, cyclohexanoic acid, lauric acid, and stearic acid; saturated dicarboxylic acids such as oxalic acid and adipic acid; aromatic carboxylic acids such as benzoic acid and para-phthalic acid; carboxylic acids in which the hydrogen atoms of the hydrocarbon groups of these carboxylic acids have been substituted with a halogen atom or an organosiylyl group, such as chloroacetic acid, dichloroacetic acid, trifluoroacetic acid, para-chlorobenzoic acid, and trimethylsilylacetic acid; unsaturated fatty acids such as acrylic acid, methacrylic acid, and oleic acid; and compounds having hydroxy groups, carbonyl groups, or amino groups in addition to carboxyl groups, namely, hydroxy acids such as lactic acid, keto acids such as acetoacetic acid, aldehyde acids such as glyoxylic acid, and amino acids such as glutamic acid.

When the isomer reducing agent comprises (2) an anhydride of carboxylic acid, suitable examples of anhydrides of carboxylic acids include acetic anhydride, propionic anhydride, and benzoic anhydride. These anhydrides of carboxylic acids may be obtained via a reaction or decomposition in the reaction system include acetyl chloride, butyryl chloride, benzoyl chloride, and other carboxylic acid halides, carboxylic acid metal salts such as zinc acetate and thallium acetate, and carboxylic esters that are decomposed by light or heat, such as (2-nitrobenzyl) propionate.

In embodiments where the isomer reducing agent comprises (3) a carboxylic silyl ester, suitable examples of carboxylic silyl esters are trialkylsilylated carboxylic acids, such as trimethylsilyl formate, trimethylsilyl acetate, triethylsilyl propionate, trimethylsilyl benzoate, and trimethylsilyl trifluoroacetate; and di-, tri-, or tetracarboxysilylates, such as dimethyldiacetoxysilane, diphenyldiacetoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane, di-t-butoxydiacetoxysilane, and silicon tetrabenzoate.

The isomer reducing agent is typically utilized in an amount ranging from 0.001 to 1 weight percent, alternatively from 0.01 to 0.1 weight percent, based on the total weight of the clustered functional polyorganosiloxane. Examples of commercially available carboxylic silyl esters suitable as the isomer reducing agent are DOW CORNING® ETS 900 or XIAMETER® OFS-1579 Silane, available from Dow Corning® Corporation of Midland, Mich.

The isomer reducing agent e), added in a sufficient amount such as from 0.001 to 1 weight percent as noted above, promotes the alpha-addition of the SiH groups of the polyorganosiloxane (ii) to the aliphatically unsaturated group of the reactive species c) over the beta-addition of the SiH groups of the polyorganosiloxane (ii) to the aliphatically unsaturated group of the reactive species c). The beta-position addition may result in the subsequent further reaction of the polyorganosiloxane to generate Si—OH and associated silicon hydroxide product (sometimes referred to as D(Oz) and/or T(Oz) units). Without being bound by any theory, it is believed that the generation of Si—OH hastens moisture cure of the polyorganosiloxanes. The relative amount of D(Oz) units generated, which correlate to the amount of beta-position addition of SiH groups of the polyorganosiloxane (ii) to the aliphatically unsaturated group of the reactive species c), may be measured by NMR.

The clustered functional polyorganosiloxane (I) produced in accordance with the present invention utilizing a sufficient amount of isomer reducing agent e) results in a reduction, and in certain embodiments at least a 10% reduction, in the amount of D(Oz) units present in the formed clustered functional polyorganosiloxane, as measured by NMR, which corresponds to a reduction, and in certain embodiments at least a 10% reduction in the beta-addition of SiH groups of the polyorganosiloxane (ii) to the aliphatically unsaturated group of the reactive species c).

The components used in the process described above for forming the clustered functional polyorganosiloxane (I) may optionally further comprise one or more additional components selected from f) a filler, g) a non-reactive resin, h) a chain extender, and i) an endcapper, or a combination thereof. Alternatively, the components used in the process may be components a), b), c) d), e) and f). Alternatively, the components used in the process may be components a), b), c) d), e), f) and h). Alternatively, the components used in the process may be components a), b), c) d), e), f) and i). Alternatively, the components used in the process may be components a), b), c) d), e), f), h) and i).

A filler may be added during the process described above. Fillers are exemplified by reinforcing and/or extending fillers such as, alumina, calcium carbonate (e.g., fumed, ground, and/or precipitated), diatomaceous earth, quartz, silica (e.g., fumed, ground, and/or precipitated), talc, zinc oxide, chopped fiber such as chopped KEVLAR®, or a combination thereof. The amount of filler will depend on various factors including the type of filler selected and the end use of the clustered functional polyorganosiloxane to be produced by the process. However, the amount of filler may be up to 20%, alternatively 1% to 20%, based on the combined weight of all the components. When the clustered functional polyorganosiloxane prepared by the process described above will be used in a silicone composition, the amount of filler may range from 10% to 20%. Alternatively, when the clustered functional polyorganosiloxane will be used in a sealant composition, the amount of filler may range from 4% to 10%.

Without wishing to be bound by theory, it is thought that when the filler is added during the process described herein, this will provide an improvement in tensile properties as compared to a prior art process in which a conventional ‘dumb-bell’ type polyorganosiloxane is formed in a multiple step process, and thereafter a filler is dispersed. Therefore, the process described in the first embodiment herein may further comprise: mixing component f), a filler, with component a) before or during step A) of the process of the first embodiment described above. Alternatively, the process of the second embodiment may further comprise mixing f) a filler with component a) before or during step A) or mixing f) a filler with the components after step I) and before or during step B) of the process of the second embodiment described above.

The above process step of adding a filler may provide a benefit with many curable groups, however, adverse reactions with clustered functional polyorganosiloxanes (for example, containing hydrolyzable groups) may still be problematic. To combat this problem, the process of the first embodiment may further comprise: mixing f) a filler and f′) a filler treating agent with component a) before or during step A) of the process of the first embodiment described above. Alternatively, the process of the second embodiment may further comprise mixing f) a filler and f′) a filler treating agent with component a) before or during step A) or mixing f) a filler and f′) a filler treating agent with the components after step A) and before or during step B) of the process of the second embodiment described above. The effective treatment of filler surfaces in situ as described above may require elevated temperature and/or vacuum conditions. These conditions may also be undesirable with thermally sensitive unsaturated functional groups and their oxygen enabled antioxidants. Therefore, the filler may be pretreated with the filler treating agent in the presence of component a) at elevated temperature and/or under vacuum. These filler treating conditions may be performed in a batch or continuous process as described, for example, in U.S. Pat. No. 6,013,701 to Kunimatsu, et al.

The resulting combination of treated filler in polyorganosiloxane is referred to as a masterbatch. Masterbatches are commercially available. The use of masterbatches allows the smooth reaction of the aliphatically unsaturated organic groups of component a) with the silicon bonded hydrogen atoms of component b) and unsaturated organic groups of component c) to be performed in a single, low shear step; leading to filled clustered functional polyorganosiloxanes with superior tensile and adhesive properties along with improved rheological and storage properties.

A masterbatch comprising a polyorganosiloxane having aliphatically unsaturated organic groups and a treated filler, with optionally a second polyorganosiloxane (having aliphatically unsaturated organic groups) of the same or differing molecular weight may be combined with components b) and c), and the resulting mixture may be sheared before addition of component d) at room temperature (RT). Reaction may then be initiated by raising the temperature to 50° C. to 100° C., alternatively 70° C. to 85° C., and maintaining the temperature until all of the SiH has reacted, as measured by the time needed for the SiH peak as observed by Fourier Transform Infra Red spectroscopy (FT-IR) at about 2170 cm⁻¹, to be reduced into the background of the spectra.

Due to thermal stability of the aliphatically unsaturated polyorganosiloxanes and filler treating agents, these processes can be carried out at higher temperatures and shear, yielding stable, reproducible masterbatches of treated filler (such as silica) in aliphatically unsaturated polyorganosiloxane (polymer) such as vinyl endblocked PDMS. Not wanting to be constrained by theory, it is believed that exposing the polymer/filler interface to high temperature and shear, optimizes polymer/filler interactions and produces stable masterbatches. By using a masterbatch, one skilled in the art can formulate a curable silicone composition at low temperature and shear, which provides the benefit of making the process more widely applicable to prepare curable silicone compositions with different cure chemistries.

The filler treating agent may be a treating agent, which is known in the art. The amount of filler treating agent may vary depending on various factors including the type and amounts of fillers selected for component f) whether the filler is treated with filler treating agent in situ or pretreated before being combined with component a). However, the components may comprise an amount ranging from 0.1% to 2% of filler treating agent, based on the weight of the filler for component f).

The filler treating agent may comprise a silane such as an alkoxysilane, an alkoxy-functional oligosiloxane, a cyclic polyorganosiloxane, a hydroxyl-functional oligosiloxane such as a dimethyl siloxane or methyl phenyl siloxane, a stearate, or a fatty acid. The alkoxysilane may have the formula: R¹⁴ _(t)Si(OR¹⁵)_((4-t)), where subscript t is 1, 2, or 3; alternatively t is 3. Each R¹⁴ is independently a monovalent organic group of 1 to 50 carbon atoms, such as a monovalent hydrocarbon group of 1 to 50 carbon atoms, alternatively 6 to 18 carbon atoms. Suitable monovalent hydrocarbon groups for R¹⁴ are exemplified by alkyl groups such as hexyl, octyl, dodecyl, tetradecyl, hexadecyl, and octadecyl; and aromatic groups such as benzyl, phenyl and phenylethyl. R¹⁴ can be a monovalent hydrocarbon group that is saturated or unsaturated and branched or unbranched. Alternatively, R¹⁴ can be a saturated, unbranched, monovalent hydrocarbon group. Each R¹⁵ may be a saturated hydrocarbon group of 1 to 4 carbon atoms, alternatively 1 to 2 carbon atoms.

Alkoxysilane filler treating agents are exemplified by hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, phenyltrimethoxysilane, phenylethyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, and a combination thereof.

Alkoxy-functional oligosiloxanes can also be used as treating agents. Alkoxy-functional oligosiloxanes and methods for their preparation are known in the art, see for example, EP 1 101 767 A2. For example, suitable alkoxy-functional oligosiloxanes include those of the formula (R¹⁶O)_(u)Si(OSiR¹⁷ ₂R¹⁸)_((4-u)). In this formula, subscript u is 1, 2, or 3, alternatively u is 3. Each R¹⁶ can be independently selected from saturated and unsaturated monovalent hydrocarbon groups of 1 to 10 carbon atoms. Each R¹⁷ can be a saturated or unsaturated monovalent hydrocarbon group having at least 11 carbon atoms. Each R¹⁸ can be an alkyl group.

Alternatively, alkoxysilanes may be used, but typically in combination with silazanes, which catalyze the less reactive alkoxysilane reaction with surface hydroxyls. Such reactions are typically performed above 100° C. with high shear with the removal of volatile by-products such as ammonia, methanol and water.

Alternatively, the filler treating agent can be any of the organosilicon compounds typically used to treat silica fillers. Examples of organosilicon compounds include, but are not limited to, organochlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, and trimethyl monochlorosilane; organosiloxanes such as hydroxy-endblocked dimethylsiloxane oligomer, hexamethyldisiloxane, and tetramethyldivinyldisiloxane; organosilazanes such as hexamethyldisilazane and hexamethylcyclotrisilazane; and organoalkoxysilanes such as methyltrimethoxysilane, C₆H₁₃Si(OCH₃)₃, C₈H₁₇Si(OC₂H₅)₃, C₁₀H₂₁Si(OCH₃)₃, C₁₂H₂₅Si(OCH₃)₃, C₁₄H₂₉Si(OC₂H₅)₃, and C₆H₅CH₂CH₂Si(OCH₃)₃, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane.

Filler treating agents for thermally conductive fillers, such as alumina or passivated aluminum nitride, may include alkoxysilyl functional alkylmethyl polysiloxanes (e.g., partial hydrolysis condensate of R¹⁶ _(o)R¹⁷ _(p)Si(OR¹⁸)_((4-O-p)) or cohydrolysis condensates or mixtures), or similar materials where the hydrolyzable group may comprise silazane, acyloxy or oximo. In all of these, a group tethered to Si, such as R¹⁶ in the formula above, is a long chain unsaturated monovalent hydrocarbon or monovalent aromatic-functional hydrocarbon. Each R¹⁷ is independently a monovalent hydrocarbon group, and each R¹⁸ is independently a monovalent hydrocarbon group of 1 to 4 carbon atoms. In the formula above, subscript o is 1, 2, or 3 and subscript p is 0, 1, or 2, with the proviso that a sum (o+p) is 1, 2, or 3.

Other filler treating agents include alkenyl functional polyorganosiloxanes. Suitable alkenyl functional polyorganosiloxanes include, but are not limited to:

where subscript q has a value up to 1,500. Other filler treating agents include mono-endcapped alkoxy functional polydiorganosiloxanes, i.e., polydiorganosiloxanes having an alkoxy group at one end. Such filler treating agents are exemplified by the formula: R²⁵R²⁶ ₂SiO(R²⁶ ₂SiO)_(u)Si(OR²⁷)₃, where subscript u has a value of 0 to 100, alternatively 1 to 50, alternatively 1 to 10, and alternatively 3 to 6. Each R²⁵ is independently selected from an alkyl group, such as methyl, ethyl, propyl, butyl, hexyl, and octyl; and an alkenyl group, such as vinyl, allyl, butenyl, and hexenyl. Each R²⁶ is independently an alkyl group such as methyl, ethyl, propyl, butyl, hexyl, and octyl. Each R²⁷ is independently an alkyl group such as methyl, ethyl, propyl, and butyl. Alternatively, each R²⁵, each R²⁶, and each R²⁷ is methyl. Alternatively, each R²⁵ is vinyl. Alternatively, each R²⁶ and each R²⁷ is methyl.

Alternatively, a polyorganosiloxane capable of hydrogen bonding is useful as a treating agent. This strategy to treating surface of a filler takes advantage of multiple hydrogen bonds, either clustered or dispersed or both, as the means to tether the compatibilization moiety to the filler surface. The polyorganosiloxane capable of hydrogen bonding has an average, per molecule, of at least one silicon-bonded group capable of hydrogen bonding. The group may be selected from: an organic group having multiple hydroxyl functionalities or an organic group having at least one amino functional group. The polyorganosiloxane capable of hydrogen bonding means that hydrogen bonding is the primary mode of attachment for the polyorganosiloxane to a filler. The polyorganosiloxane may be incapable of forming covalent bonds with the filler. The polyorganosiloxane capable of hydrogen bonding may be selected from the group consisting of a saccharide-siloxane polymer, an amino-functional polyorganosiloxane, and a combination thereof. Alternatively, the polyorganosiloxane capable of hydrogen bonding may be a saccharide-siloxane polymer.

The non-reactive silicone resin g) useful herein contains monofunctional units represented by R¹⁹ ₃SiO_(1/2) and tetrafunctional units represented by SiO_(4/2). R¹⁹ represents a nonfunctional monovalent organic group such as a hydrocarbon group. The silicone resin is soluble in liquid hydrocarbons such as benzene, toluene, xylene, heptane and the like or in liquid organosilicon compounds such as a low viscosity cyclic and linear polydiorganosiloxanes.

In the R¹⁹ ₃SiO_(1/2) unit, R¹⁹ may be a monovalent hydrocarbon group containing up to 20 carbon atoms, alternatively 1 to 10 carbon atoms. Examples of suitable monovalent hydrocarbon groups for R¹⁹ include alkyl groups, such as methyl, ethyl, propyl, butyl pentyl, octyl, undecyl and octadecyl; cycloaliphatic radicals, such as cyclohexyl and cyclohexenylethyl; and aryl radicals such as phenyl, tolyl, xylyl, benzyl and 2-phenylethyl. Organic groups for R¹⁵ are exemplified by the hydrocarbon groups above modified such that where a non-reactive substituent has replaced a hydrogen atom, for example, the nonreactive substituents may include but are not limited to halogen and cyano. Typical organic groups that can be represented by R¹⁹ include but are not limited to chloromethyl and 3,3,3-trifluoropropyl.

The molar ratio of the R¹⁹ ₃SiO_(1/2) and SiO_(4/2) units in the silicone resin may range from 0.5/1 to 1.5/1, alternatively from 0.6/1 to 0.9/1. These mole ratios are conveniently measured by Silicon 29 Nuclear Magnetic Spectroscopy (²⁹Si NMR). This technique is capable of quantitatively determining the concentration of R¹⁹ ₃SiO_(1/2) (“M”) and SiO_(4/2) (“Q”) units derived from the silicone resin, in addition to the total hydroxyl content of the silicone resin.

The silicone resin may further comprise 2.0% or less, alternatively 0.7% or less, alternatively 0.3% or less, of terminal units represented by the formula XSiO_(3/2), where X represents hydroxyl or a hydrolyzable group exemplified by alkoxy such as methoxy and ethoxy. The concentration of hydrolyzable groups present in the silicone resin can be determined using FT-IR.

The weight average molecular weight, M_(W), will depend at least in part on the molecular weight of the silicone resin and the type(s) of hydrocarbon groups, represented by R¹⁵, that are present in this component. M_(W) as used herein represents the molecular weight measured using gel permeation chromatography (GPC), when the peak representing the neopentamer is excluded form the measurement. The M_(W) of the silicone resin may range from 12,000 to 30,000 g/mole, typically 17,000 to 22,000 g/mole.

The silicone resin can be prepared by any suitable method. Silicone resins of this type have been prepared by cohydrolysis of the corresponding silanes or by silica hydrosol capping methods known in the art. The silicone resin may be prepared by the silica hydrosol capping processes of Daudt, et al., U.S. Pat. No. 2,676,182; of Rivers-Farrell et al., U.S. Pat. No. 4,611,042; and of Butler, U.S. Pat. No. 4,774,310.

The intermediates used to prepare the silicone resin are typically triorganosilanes of the formula R¹⁹ ₃SiX′, where X′ represents a hydrolyzable group, and either a silane with four hydrolyzable groups such as halogen, alkoxy or hydroxyl, or an alkali metal silicate such as sodium silicate.

It is desirable that the silicon-bonded hydroxyl groups (i.e., HOR¹⁹SiO_(1/2) or HOSiO_(3/2) groups) in the silicone resin be below 0.7% based on the total weight of the silicone resin, alternatively below 0.3%. Silicon-bonded hydroxyl groups formed during preparation of the silicone resin may be converted to trihydrocarbylsiloxy groups or a hydrolyzable group by reacting the silicone resin with a silane, disiloxane or disilazane containing the appropriate terminal group. Silanes containing hydrolyzable groups are typically added in excess of the quantity required to react with the silicon-bonded hydroxyl groups of the silicone resin.

Component h) is a chain extender. The chain extender may be a polydiorganosiloxane terminated at both ends with hydrogen atoms. An exemplary chain extender may have the formula (XVII): HR²⁰ ₂Si—(R²⁰ ₂SiO)_(v)—SiR²⁰ ₂H, where each R²⁰ is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl, and benzyl. Subscript v has an average value ranging from 0 to 400, alternatively 10 to 100.

Whether to use a chain extender, and the amount used when present, depends on various factors including the degree of crosslinking inherent in the system. For example, when starting with a polyorganosiloxane for component a) which has a relatively low average DP, e.g., average DP ranging from 60 to 400, then 50 mole % to 80 mole % of the SiH content in all of the components combined may come from the chain extender, alternatively 70 mole %. When using longer vinyl endblocked polymer (average DP>400) then lower levels are effective, e.g., 25 mole % to 50 mole % of SiH from chain extending molecules, preferably 40 mole %.

Component i) is an endcapper. The endcapper may be a polydiorganosiloxane having one silicon-bonded hydrogen atom per molecule. An exemplary endcapper may have the formula R⁵ ₃SiO—(R⁵ ₂SiO)_(e)—SiR⁵ ₂H. In this formula, each R⁵ is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl and benzyl; and subscript e has a value ranging from 0 to 10, alternatively 1 to 10, and alternatively 1. Another exemplary endcapper may have the formula R⁶ ₃SiO—(R⁶ ₂SiO)_(f)—(HR⁶SiO)—SiR⁶ ₃. In this formula, each R⁶ is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl and benzyl. Subscript f has a value ranging from 0 to 10, alternatively 0.

The endcapper may provide the benefit of producing a looser network of higher tensile properties when used as a mole percentage of the available SiH in the system. The amount of endcapper added may range from 0 to 15%, alternatively 2% to 15%, and alternatively 10%, based on the combined weight of all components used in the process.

A secondary benefit of having an endcapper in the process is initial reduction in viscosity prior to reaction, which may facilitate the reaction and reduce the tendency for gelation due to insufficient mixing and local gel formation.

Alternatively, one of a chain extender or an endcapper is used; i.e., in this instance, the chain extender and the endcapper are not in combination with each other.

The endcapper may provide the benefit of producing a looser network of higher tensile properties when used as a mole percentage of the available SiH in the system. The amount of endcapper added may range from 0 to 15%, alternatively 2% to 15%, and alternatively 10%, based on the combined weight of all components used in the process.

A secondary benefit of having a chain extender or an endcapper in the process is initial reduction in viscosity prior to reaction, which may facilitate the reaction and reduce the tendency for gelation due to insufficient mixing and local gel formation. Using a chain extender or an endcapper may be especially beneficial when using relatively high molecular weight polyorganosiloxanes for component a) (e.g., average DP greater than 400) and when a filler is present.

The weight percent of silicon bonded hydrogen atoms in the components/weight percent of unsaturated organic groups capable of undergoing hydrosilylation in the components (commonly referred to as SiH_(tot)/Vi_(tot) ratio) may range from 1/1.4 to 1/1, alternatively 1/1.2 to 1/1.1. In this ratio, SiH_(tot) refers to the amount of silicon bonded hydrogen atoms in component b) in combination with the amount of silicon bonded hydrogen atoms in components h) and/or i), if present. Vi_(tot) refers to the total amount of aliphatically unsaturated organic groups in components a) and c) combined.

Component j) is a catalyst inhibitor. Component j) may optionally be added after step 1) in the method of the process of the first embodiment described above or after step II) in the method of the process of the second embodiment described above to stop the reaction and stabilize the clustered functional polyorganosiloxane prepared by the process described above. Some examples of suitable catalyst inhibitors include ethylenically or aromatically unsaturated amides, acetylenic compounds such as 2-ethynyl-isopropanol, 2-ethynyl-butane-2-ol, 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,5-hexadiene, 1,6-heptadiene; 3,5-dimethyl-1-hexen-1-yne; 3-ethyl-3-buten-1-yne or 3-phenyl-3-buten-1-yne; ethylenically unsaturated isocyanates; silylated acetylenic alcohols exemplified by trimethyl (3,5-dimethyl-1-hexyn-3-oxy)silane, dimethyl-bis-(3-methyl-1-butyn-oxy) silane, methylvinylbis(3-methyl-1-butyn-3-oxy)silane, and ((1,1-dimethyl-2-propynyl)oxy)trimethylsilane; unsaturated hydrocarbon diesters; conjugated ene-ynes exemplified by 2-isobutyl-1-butene-3-yne, 3,5-dimethyl-3-hexene-1-yne, 3-methyl-3-pentene-1-yne, 3-methyl-3-hexene-1-yne, 1-ethynylcyclohexene, 3-ethyl-3-butene-1-yne, and 3-phenyl-3-butene-1-yne; olefinic siloxanes such as 1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethyl cyclotetrasiloxane, or 1,3-divinyl-1,3-diphenyldimethyldisiloxane; 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; a mixture of a conjugated ene-yne as described above and an olefinic siloxane as described above; hydroperoxides; nitriles and diaziridines; unsaturated carboxylic esters exemplified by diallyl maleate, dimethyl maleate, diethyl fumarate, diallyl fumarate, and bis-2-methoxy-1-methylethylmaleate, mono-octylmaleate, mono-isooctylmaleate, mono-allyl maleate, mono-methyl maleate, mono-ethyl fumarate, mono-allyl fumarate, and 2-methoxy-1-methylethylmaleate; fumarates such as diethylfumarate; fumarate/alcohol mixtures wherein the alcohol is benzyl alcohol or 1-octanol and ethenyl cyclohexyl-1-ol; a nitrogen-containing compound such as tributylamine, tetramethylethylenediamine, benzotriazole; a similar phosphorus-containing compound such as triphenylphosphine; a sulphur-containing compound; a hydroperoxy compound; or a combination thereof.

The inhibitors are used in an amount effective to deactivate component d) the hydrosilylation catalyst. The amount will vary depending on the type and amount of catalyst and the type of inhibitor selected, however, the amount may range from 0.001 to 3 parts by weight, and alternatively from 0.01 to 1 part by weight per 100 parts by weight of component a).

Optional Component (II) is a silicone reactive diluent. The silicone reactive diluent (II) aids in dispensing of the curable silicone composition by reducing the viscosity of the curable silicone composition to make it more flowable.

In certain embodiments, when present, the amount of silicone reactive diluent (II) utilized ranges from 20 to 90 weight percent, alternatively from 40 to 70 weight percent, alternatively from 55 to 80 weight percent, alternatively from 55 to 75 weight percent, alternatively 70 weight percent, based on the total silicone matrix weight of thermally conductive thermal radical cure silicone composition. The silicone matrix weight, as defined herein, refers to the total weight of the clustered functional polyorganosiloxane (I) and the silicone reactive diluent (II).

The silicone reactive diluent (II) may be a monofunctional silicone reactive diluent, a difunctional silicone reactive diluent, a polyfunctional silicone reactive diluent, or a combination thereof. The silicone reactive diluent selected will depend on various factors including the curable groups. However, examples of suitable silicone reactive diluents include an acrylate, an anhydride such as a maleic anhydride or methacrylic anhydride, an epoxy such as a monofunctional epoxy compound, a methacrylate such as glycidyl methacrylate, an oxetane, a vinyl acetate, a vinyl ester, a vinyl ether, a fluoro alkyl vinyl ether, a vinyl pyrrolidone such as N-vinyl pyrrolidone, a styrene, or a combination thereof.

A first embodiment of the silicone reactive diluent (II) may be formed as the reaction product of a reaction of:

-   -   a) a polyorganohydrogensiloxane having an average of 10 to 200         silicon atoms per molecule; and     -   b) a reactive species having, per molecule, at least 1         aliphatically unsaturated organic group and 1 or more curable         groups;     -   in the presence of c) an isomer reducing agent and d) a         hydrosilylation catalyst and e) inhibitor for hydrosilylation         catalyst.

In certain other embodiments, additional optional components may also be included in the silicone reactive diluent (II) of the first embodiment.

Component a) is a polyorganohydrogensiloxane having an average of 10 to 200 silicon atoms per molecule. Component a) may be branched, or linear. Component a) may be monofunctional (i.e., includes one silicon-bonded hydrogen atom), a difunctional (i.e., includes two silicon-bonded hydrogen atoms), a polyfunctional (i.e., includes more than two silicon-bonded hydrogen atoms), or a combination thereof. Component a) may be a combination comprising two or more polyorganohydrogensiloxanes each having an average of 10 to 200 silicon atoms per molecule that differ in at least one of the following properties: structure, viscosity, degree of polymerization, and sequence.

In certain embodiments, component a) may be a polydiorganosiloxane terminated at both ends with hydrogen atoms. One exemplary polydiorganosiloxane terminated at both ends with hydrogen atoms may have the formula HR₂Si—(R₂SiO)_(a)—SiR₂H, where each R is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl, and benzyl. Subscript a has an average value ranging from 0 to 400, alternatively 10 to 200.

Alternatively, component a) may be a branched polyorganohydrogensiloxane. The branched polyorganohydrogensiloxane for component b) may have the formula Si—(OSiR² ₂)_(b)(OSiHR²)_(b′)(OSiR² ₃)_(c)(OSiR² ₂H)_((4-c)), in which each R² is independently a monovalent organic group free of aliphatic unsaturation, subscript b has a value ranging from 0 to 10, subscript b′ has a value ranging from 0 to 10, and subscript c has a value ranging from 0 to 1.

Alternatively, subscript b may be 0. When subscript b′ is 0, then subscript c is also 0. Monovalent organic groups suitable for R² include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Component b) is a reactive species. The reactive species b) may be any species that can provide the curable groups in the silicone reactive diluent. The reactive species has an average, per molecule, of at least one aliphatically unsaturated organic group that is capable of undergoing an addition reaction with a silicon bonded hydrogen atom of component a). Component b) further comprises one or more radical curable groups per molecule. The radical curable groups are functional (reactive) groups that render the silicone reactive diluent radiation curable. The radical curable groups on component b) may be selected from acrylate groups and methacrylate groups and combinations thereof.

For example, in certain embodiments, component b) may comprise a silane of formula R³ _(d)SiR⁴ _((3-d)); in which subscript d has a value ranging from 1 to 3, each R³ is independently an aliphatically unsaturated organic group, and each R⁴ is independently selected from an organic group containing an acrylate group and a methacrylate group.

Alternatively, component b) may comprise an organic compound (which does not contain a silicon atom). The organic compound for component b) may have an average, per molecule, of 1 to 2 aliphatically unsaturated organic groups, such as alkenyl or alkynyl groups, and one or more reactive groups selected from an acrylate group and a methacrylate group. Examples of suitable organic compounds for component b) include, but are not limited to, allyl acrylate and allyl methacrylate (AMA), and combinations thereof.

The amount of component b) depends on various factors including the type, amount, and SiH content of component a) and the type of component b) selected. However, the amount of component b) is sufficient to make SiH_(tot)/Vi_(tot) range from 1/1 to 1/1.4, alternatively 1/1.2 to 1.1/1. The ratio SiH_(tot)/Vi_(tot) means the weight percent of total amount of silicon bonded hydrogen atoms on component b) divided by the total weight percent of aliphatically unsaturated organic groups on component a).

Component c) is an isomer reducing agent. In certain embodiments, the isomer reducing agent comprises a carboxylic acid compound. The carboxylic acid compound may comprise (1) carboxylic acid, (2) an anhydride of a carboxylic acid, (3) a carboxylic silyl ester, and/or (4) a substance that will produce the above-mentioned carboxylic acid compounds (i.e., (1), (2), and/or (3)) through a reaction or decomposition in the reaction of the method. It is to be appreciated that a mixture of one or more of these carboxylic acid compounds may be utilized as the isomer reducing agent. For example, a carboxylic silyl ester may be utilized in combination with an anhydride of a carboxylic acid as the isomer reducing agent. In addition, a mixture within one or more types of carboxylic acid compounds may be utilized as the isomer reducing agent. For example, two different carboxylic silyl esters may be utilized in concert, or two carboxylic silyl esters may be utilized in concert with an anhydride of a carboxylic acid.

When the isomer reducing agent c) comprises (1) carboxylic acid, any carboxylic acid having carboxyl groups may be utilized. Suitable examples of carboxylic acids include saturated carboxylic acids, unsaturated carboxylic acids, monocarboxylic acids, and dicarboxylic acids. A saturated or unsaturated aliphatic hydrocarbon group, aromatic hydrocarbon group, halogenated hydrocarbon group, hydrogen atom, or the like is usually selected as the portion other than the carboxyl groups in these carboxylic acids. Specific examples of suitable carboxylic acids include saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, hexanoic acid, cyclohexanoic acid, lauric acid, and stearic acid; saturated dicarboxylic acids such as oxalic acid and adipic acid; aromatic carboxylic acids such as benzoic acid and para-phthalic acid; carboxylic acids in which the hydrogen atoms of the hydrocarbon groups of these carboxylic acids have been substituted with a halogen atom or an organosiylyl group, such as chloroacetic acid, dichloroacetic acid, trifluoroacetic acid, para-chlorobenzoic acid, and trimethylsilylacetic acid; unsaturated fatty acids such as acrylic acid, methacrylic acid, and oleic acid; and compounds having hydroxy groups, carbonyl groups, or amino groups in addition to carboxyl groups, namely, hydroxy acids such as lactic acid, keto acids such as acetoacetic acid, aldehyde acids such as glyoxylic acid, and amino acids such as glutamic acid.

When the isomer reducing agent c) comprises (2) an anhydride of carboxylic acid, suitable examples of anhydrides of carboxylic acids include acetic anhydride, propionic anhydride, and benzoic anhydride. These anhydrides of carboxylic acids may be obtained via a reaction or decomposition in the reaction system include acetyl chloride, butyryl chloride, benzoyl chloride, and other carboxylic acid halides, carboxylic acid metal salts such as zinc acetate and thallium acetate, and carboxylic esters that are decomposed by light or heat, such as (2-nitrobenzyl) propionate.

In embodiments where the isomer reducing agent c) comprises (3) a carboxylic silyl ester, suitable examples of carboxylic silyl esters are trialkylsilylated carboxylic acids, such as trimethylsilyl formate, trimethylsilyl acetate, triethylsilyl propionate, trimethylsilyl benzoate, and trimethylsilyl trifluoroacetate; and di-, tri-, or tetracarboxysilylates, such as dimethyldiacetoxysilane, diphenyldiacetoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane, di-t-butoxydiacetoxysilane, and silicon tetrabenzoate.

The isomer reducing agent c) is typically utilized in an amount ranging from 0.001 to 1 weight percent, alternatively from 0.01 to 0.1 weight percent, based on the total weight of the formed silicone reactive diluent (II) of the first embodiment. Examples of commercially available carboxylic silyl esters suitable as the isomer reducing agent are DOW CORNING® ETS 900 or XIAMETER® OFS-1579 Silane, available from Dow Corning® Corporation of Midland, Mich.

The isomer reducing agent c), added in a sufficient amount such as from 0.001 to 1 weight percent as noted above, promotes the alpha-addition of the SiH groups of the polydiorganosiloxane a) to the aliphatically unsaturated group of the reactive species b) over the beta-addition of the SiH groups of the polydiorganosiloxane (a) to the aliphatically unsaturated group of the reactive species b). The beta-position addition may result in the subsequent further reaction of the polyorganosiloxane to generate Si—OH and associated silicon hydroxide product (sometimes referred to as D(Oz) and/or T(Oz) units). Without being bound by any theory, it is believed that the generation of Si—OH hastens moisture cure of the polydiorganosiloxanes. The relative amount of D(Oz) units generated, which correlate to the amount of beta-position addition of SiH groups of the polyorganosiloxane (ii) to the aliphatically unsaturated group of the reactive species c), may be measured by NMR.

Component d) is a hydrosilylation catalyst which accelerates the reaction of components a) and b). Component d) may be added in an amount sufficient to promote the reaction of components a) and b), and this amount may be, for example, sufficient to provide 0.1 parts per million (ppm) to 1000 ppm of platinum group metal, alternatively 1 ppm to 500 ppm, alternatively 2 ppm to 200, alternatively 5 ppm to 20 ppm, based on the combined weight of all components used in the process.

Suitable hydrosilylation catalysts are known in the art and commercially available. Component d) may comprise a platinum group metal selected from platinum (Pt), rhodium, ruthenium, palladium, osmium or iridium metal or organometallic compound thereof, or a combination thereof. Component d) is exemplified by compounds such as chloroplatinic acid, chloroplatinic acid hexahydrate, platinum dichloride, and complexes of said compounds with low molecular weight organopolysiloxanes or platinum compounds microencapsulated in a matrix or coreshell type structure. Complexes of platinum with low molecular weight organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. These complexes may be microencapsulated in a resin matrix. Alternatively, the catalyst may comprise 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum. When the catalyst is a platinum complex with a low molecular weight organopolysiloxane, the amount of catalyst may range from 0.04% to 0.4% based on the combined weight of the components used in the process.

Suitable hydrosilylation catalysts for component d) are described in, for example, U.S. Pat. Nos. 3,159,601; 3,220,972; 3,296,291; 3,419,593; 3,516,946; 3,814,730; 3,989,668; 4,784,879; 5,036,117; and 5,175,325 and EP 0 347 895 B. Microencapsulated hydrosilylation catalysts and methods of preparing them are known in the art, as exemplified in U.S. Pat. Nos. 4,766,176; and 5,017,654.

Component e) is a catalyst inhibitor, which is added to deactivate component d) (the hydrosilylation catalyst) and stabilize the formed silicone reactive diluents. Some examples of suitable catalyst inhibitors include ethylenically or aromatically unsaturated amides, acetylenic compounds such as 2-ethynyl-isopropanol, 2-ethynyl-butane-2-ol, 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,5-hexadiene, 1,6-heptadiene; 3,5-dimethyl-1-hexen-1-yne; 3-ethyl-3-buten-1-yne or 3-phenyl-3-buten-1-yne; ethylenically unsaturated isocyanates; silylated acetylenic alcohols exemplified by trimethyl (3,5-dimethyl-1-hexyn-3-oxy)silane, dimethyl-bis-(3-methyl-1-butyn-oxy)silane, methylvinylbis(3-methyl-1-butyn-3-oxy)silane, and ((1,1-dimethyl-2-propynyl)oxy)trimethylsilane; unsaturated hydrocarbon diesters; conjugated ene-ynes exemplified by 2-isobutyl-1-butene-3-yne, 3,5-dimethyl-3-hexene-1-yne, 3-methyl-3-pentene-1-yne, 3-methyl-3-hexene-1-yne, 1-ethynylcyclohexene, 3-ethyl-3-butene-1-yne, and 3-phenyl-3-butene-1-yne; olefinic siloxanes such as 1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethyl cyclotetrasiloxane, or 1,3-divinyl-1,3-diphenyldimethyldisiloxane; 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; a mixture of a conjugated ene-yne as described above and an olefinic siloxane as described above; hydroperoxides; nitriles and diaziridines; unsaturated carboxylic esters exemplified by diallyl maleate, dimethyl maleate, diethyl fumarate, diallyl fumarate, and bis-2-methoxy-1-methylethylmaleate, mono-octylmaleate, mono-isooctylmaleate, mono-allyl maleate, mono-methyl maleate, mono-ethyl fumarate, mono-allyl fumarate, and 2-methoxy-1-methylethylmaleate; fumarates such as diethylfumarate; fumarate/alcohol mixtures wherein the alcohol is benzyl alcohol or 1-octanol and ethenyl cyclohexyl-1-ol; a nitrogen-containing compound such as tributylamine, tetramethylethylenediamine, benzotriazole; a similar phosphorus-containing compound such as triphenylphosphine; a sulphur-containing compound; a hydroperoxy compound; or a combination thereof.

The inhibitors are used in an amount effective to deactivate component d) the hydrosilylation catalyst. The amount will vary depending on the type and amount of catalyst and the type of inhibitor selected, however, the amount may range from 0.001 to 3 parts by weight, and alternatively from 0.01 to 1 part by weight per 100 parts by weight of component a).

In addition to Components a)-e), other optional components may be utilized in forming the silicone reactive diluents. For example, in certain embodiments, the silicone reactive diluent may further include f) a polymerization inhibitor and g) an endcapper.

Optional component 0 is a polymerization inhibitor. The unsaturated groups (e.g., methacrylate, acrylate, vinyl or allyl) can autopolymerize via unwanted radical process. These radical process can be mitigated by the addition of polymerization inhibitors. Examples of suitable polymerization inhibitors for acrylate and methacrylate curable groups include, but are not limited to: 2,6,-Di-tert-butyl-4-(dimethylaminomethyl)phenol (DBAP), hydroquinone (HQ); 4-methoxyphenol (MEHQ); 4-ethoxyphenol; 4-propoxyphenol; 4-butoxyphenol; 4-heptoxyphenol; butylated hydroxytoluene (BHT); hydroquinone monobenzylether; 1,2-dihydroxybenzene; 2-methoxyphenol; 2,5-dichlorohydroquinone; 2,5-di-tert-butylhydroquinone; 2-acetylhydroquinone; hydroquinone monobenzoate; 1,4-dimercaptobenzene; 1,2-dimercaptobenzene; 2,3,5-trimethylhydroquinone; 4-aminophenol; 2-aminophenol; 2-N, N-dimethylaminophenol; 2-mercaptophenol; 4-mercaptophenol; catechol monobutylether; 4-ethylaminophenol; 2,3-dihydroxyacetophenone; pyrogallol-1,2-dimethylether; 2-methylthiophenol; t-butyl catechol; di-tert-butylnitroxide; di-tert-amylnitroxide; 2,2,6,6-tetramethyl-piperidinyloxy; 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy; 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy; 4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy; 4-amino-2,2,6,6-tetramethyl-piperidinyloxy; 4-ethanoloxy-2,2,6,6-tetramethyl-piperidinyloxy; 2,2,5,5-tetramethyl-pyrrolidinyloxy; 3-amino-2,2,5,5-tetramethyl-pyrrolidinyloxy; 2,2,5,5-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy; 2,2,5,5-tetramethyl-3-pyrrolinyl-1-oxy-3-carboxylic acid; 2,2,3,3,5,5,6,6-octamethyl-1,4-diazacyclohexyl-1,4-dioxy; salts of 4-nitrosophenolate; 2-nitrosophenol; 4-nitrosophenol; copper dimethyldithiocarbamate; copper diethyldithiocarbamate; copper dibutyldithiocarbamate; copper salicylate; methylene blue; iron; phenothiazine (PTZ); 3-oxophenothiazine; 5-oxophenothiazine; phenothiazine dimer; 1,4-benzenediamine; N-(1,4-dimethylpentyl)-N′-phenyl-1,4-benzenediamine; N-(1,3-dimethylbutyl)-N′-phenyl-1,4-benzenediamine; N-nitrosophenylhydroxylamine and salts thereof; nitric oxide; nitrobenzene; p-benzoquinone; pentaerythrityl tetrakis(3-laurylthiopropionate); dilauryl thiodipropionate; distearyll thiodipropionate; ditridecyl thiodipropionate; tetrakis[methylene 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; N,N′-hexamethyl (3,5-di-tertbutyl-4-hydroxyhydrocinnamamide); iso-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; 2,2′-ethylidenebis-(4,6-di-tert-butylphenol); 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; 4,6-bis(octylthiomethyl)-o-cresol; triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate; tris-(3,5-di-tert-butylhydroxybenzyl) isocyanurate; tris(2,4-di-tert-butylphenyl) phosphate; distearyl pentaerythritol diphosphite; bis(2,4-di-tert-butyl phenyl)pentaerythritol diphosphite; 2,5-di-tert-amyl-hydroquinone; or isomers thereof; combinations of two or more thereof; or combinations of one or more of the above with molecular oxygen. When present, the polymerization inhibitor may be added to the curable silicone composition in an amount ranging from 100 ppm to 4,000 ppm.

Optional component g) is an endcapper. The endcapper may be a polydiorganosiloxane having one silicon-bonded hydrogen atom per molecule. An exemplary endcapper may have the formula R⁵ ₃SiO—(R⁵ ₂SiO)_(e)—SiR⁵ ₂H. In this formula, each R⁵ is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl and benzyl; and subscript e has a value ranging from 0 to 10, alternatively 1 to 10, and alternatively 1. Another exemplary endcapper may have the formula R⁶ ₃SiO—(R⁶ ₂SiO)_(f)—(HR⁶SiO)—SiR⁶ ₃. In this formula, each R⁶ is independently a monovalent hydrocarbon group exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl, xylyl and benzyl. Subscript f has a value ranging from 0 to 10, alternatively 0.

The endcapper may provide the benefit of producing a looser network of higher tensile properties when used as a mole percentage of the available SiH in the system. The amount of endcapper added may range from 0 to 15%, alternatively 2% to 15%, and alternatively 10%, based on the combined weight of all components used in the process.

A secondary benefit of having an endcapper in the process is initial reduction in viscosity prior to reaction, which may facilitate the reaction and reduce the tendency for gelation due to insufficient mixing and local gel formation.

The weight percent of silicon bonded hydrogen atoms in the components/weight percent of unsaturated organic groups capable of undergoing hydrosilylation in the components (commonly referred to as SiH_(tot)/Vi_(tot) ratio) may range from 1/1.4 to 1/1, alternatively 1/1.2 to 1/1.1. In this ratio, SiH_(tot) refers to the amount of silicon bonded hydrogen atoms in any of the components of the silicone reactive diluent. Vi_(tot) refers to the total amount of aliphatically unsaturated organic groups in the silicone reactive diluent.

In certain embodiments, the silicone reactive diluent in accordance with the present invention is formed by:

1) concurrently reacting components comprising:

-   -   a) a polyorganohydrogensiloxane having an average of 10 to 200         silicon atoms per molecule; and     -   b) a reactive species having, per molecule, at least 1         aliphatically unsaturated organic group and 1 or more curable         groups;     -   in the presence of c) an isomer reducing agent and d) a         hydrosilylation catalyst, and optionally f) a polymerization         inhibitor and g) an endcapper.

The resulting mixture of a), b), c), d) and optionally f) and g) may be sheared before addition of component c) at room temperature. The reaction may then be initiated by raising the temperature to a range from 35° C. to 100° C., alternatively 50° C. to 85° C., and maintaining the temperature until all of the SiH has reacted, as measured by the time needed for the SiH peak as observed by Fourier Transform Infra Red spectroscopy (FT-IR) at about 2170 cm⁻¹, to be reduced into the background of the spectra.

Next, the catalyst inhibitor e) is added to the resulting mixture to deactivate the hydrosilylation catalyst c). In certain embodiments, the introduction of the catalyst inhibitor e) is done after reducing the temperature of the reaction mixture of a), b), c), d) and optionally f) and g) below the minimum reaction temperature of 50° C., such as at room temperature. The formed silicone reactive diluent (II) of the first embodiment may be stored for subsequent use.

In an alternative or second embodiment, the silicone reactive diluent (II) may be formed as the reaction product of a reaction of:

-   -   a) a siloxane compound according to the formula:

-   -   wherein:         -   R is a monovalent hydrocarbon having 1 to 6 carbon atoms,         -   R′ is a divalent hydrocarbon having 3 to 12 carbon atoms.         -   R″ is H or CH₃, and         -   the subscripts m and n each have a value from 1 to 10, and     -   b) a polyorganosiloxane having an average, per molecule, of at         least 2 aliphatically unsaturated organic groups,     -   in the presence of c) a first hydrosilylation catalyst and d) an         inhibitor for the first hydrosilylation catalyst, as well as         other additional optional components.

Component b) of the silicone reactive diluent (II) of the second embodiment is a polyorganosiloxane having an average, per molecule, of at least 2 aliphatically unsaturated organic groups, which are capable of undergoing a hydrosilylation reaction with a silicon bonded hydrogen atom of the siloxane compound a). Component b) may have a linear or branched structure. Alternatively, component b) may have a linear structure. Component b) may be a combination comprising two or more polyorganosiloxanes that differ in at least one of the following properties: structure, viscosity, degree of polymerization, and sequence.

Component b) has a minimum average degree of polymerization (average DP) of 10. Alternatively, average DP of component b) may range from 10 to 1000 alternatively 100 to 200. The distribution DP of polyorganosiloxanes of component a) can be bimodal. For example, component b) may comprise one alkenyl terminated polydiorganosiloxane with a DP of 2 and another alkenyl terminated polydiorganosiloxane with a DP higher than 10, provided that average DP of the polydiorganosiloxanes ranges from 10 to 1000. However, suitable polyorganosiloxanes for use in component b) have a minimum degree of polymerization (DP) of 10, provided that polyorganosiloxanes with DP less than 10 are combined with polyorganosiloxanes having DP greater than 10. Suitable polydiorganosiloxanes for component a) are known in the art and are commercially available. For example, Dow Corning® SFD-128 has DP ranging from 800 to 1000, Dow Corning® SFD-120 has DP ranging from 600 to 700, Dow Corning® 7038 has DP of 100, and Dow Corning® SFD-119 has DP of 150. All of these are vinyl-terminated polydimethylsiloxanes are commercially available from Dow Corning® Corporation of Midland, Mich., USA. When component b) has a bimodal distribution, the polyorganosiloxane with the lower DP (low DP polyorganosiloxane) is present in a lower amount than the polyorganosiloxane with the higher DP (high DP polyorganosiloxane). For example, in a bimodal distribution, the ratio of low DP polyorganosiloxane/high DP polyorganosiloxane may range from 10/90 to 25/75.

Component b) is exemplified by polyorganosiloxanes of formula (I), formula (II), or a combination thereof. Formula (I) is R¹ ₂R²SiO(R¹ ₂SiO)_(a)(R¹R²SiO)_(b)SiR¹ ₂R², and formula (II) is R¹ ₃SiO(R¹ ₂SiO)_(c)(R¹R²SiO)_(d)SiR¹ ₃. In these formulae, each R¹ is independently a monovalent organic group free of aliphatic unsaturation, each R² is independently an aliphatically unsaturated organic group, subscript a has an average value ranging from 2 to 1000, subscript b has an average value ranging from 0 to 1000, subscript c has an average value ranging from 0 to 1000, and subscript d has an average value ranging from 4 to 1000. In formulae (I) and (II), 10≤(a+b)≤1000 and 10≤(c+d)≤1000.

Suitable monovalent organic groups for R¹ include, but are not limited to, monovalent hydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl. Each R² is independently an aliphatically unsaturated monovalent organic group. R² may be an aliphatically unsaturated monovalent hydrocarbon group exemplified by alkenyl groups such as vinyl, allyl, propenyl, and butenyl; and alkynyl groups such as ethynyl and propynyl.

Component b) may comprise a polydiorganosiloxane such as i) dimethylvinylsiloxy-terminated polydimethylsiloxane, ii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane), iii) dimethylvinylsiloxy-terminated polymethylvinylsiloxane, iv) trimethylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane), v) trimethylsiloxy-terminated polymethylvinylsiloxane, vi) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylphenylsiloxane), vii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/diphenylsiloxane), viii) phenyl, methyl, vinyl-siloxy-terminated polydimethylsiloxane, ix) dimethylhexenylsiloxy-terminated polydimethylsiloxane, x) dimethylhexenylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), xi) dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane, xii) trimethylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), or xiii) a combination thereof.

The relative amounts of the siloxane compound a) and the polyorganosiloxane b) in the silicone reactive diluent (II) of the second embodiment may vary such that the SiH:vinyl weight ratio ranges from 0.8:1 to 1:1.

Suitable hydrosilylation catalysts c) and inhibitors for the hydrosilylation catalyst d) that may be used in forming the silicone reactive diluent (II) in the second embodiment include each of the hydrosilylation catalysts and inhibitors d) described above and not repeated herein.

In addition to Components a)-d), other optional components may be utilized in forming the silicone reactive diluent (II) according to the second embodiment, including f) a polymerization inhibitor and g) an endcapper, the descriptions of which are the same as provided as optional components f) and g) of the silicone reactive diluent (II) of the first embodiment above and not repeated herein.

Component (III) is a filler that includes a thermally conductive filler. In certain embodiments, in addition to thermally conductive filler, the filler (III) may also comprise a reinforcing filler, an extending filler, or a combination thereof.

Thermally conductive filler may be both thermally conductive and electrically conductive. Alternatively, thermally conductive filler may be thermally conductive and electrically insulating. Thermally conductive filler may be selected from the group consisting of aluminum nitride, aluminum oxide, aluminum trihydrate, barium titanate, beryllium oxide, boron nitride, carbon fibers, diamond, graphite, magnesium hydroxide, magnesium oxide, metal particulate, onyx, silicon carbide, tungsten carbide, zinc oxide, and a combination thereof. Thermally conductive filler may comprise a metallic filler, an inorganic filler, a meltable filler, or a combination thereof. Metallic fillers include particles of metals and particles of metals having layers on the surfaces of the particles. These layers may be, for example, metal nitride layers or metal oxide layers on the surfaces of the particles. Suitable metallic fillers are exemplified by particles of metals selected from the group consisting of aluminum, copper, gold, nickel, silver, and combinations thereof, and alternatively aluminum. Suitable metallic fillers are further exemplified by particles of the metals listed above having layers on their surfaces selected from the group consisting of aluminum nitride, aluminum oxide, copper oxide, nickel oxide, silver oxide, and combinations thereof. For example, the metallic filler may comprise aluminum particles having aluminum oxide layers on their surfaces.

Inorganic fillers are exemplified by onyx; aluminum trihydrate, metal oxides such as aluminum oxide, beryllium oxide, magnesium oxide, and zinc oxide; nitrides such as aluminum nitride and boron nitride; carbides such as silicon carbide and tungsten carbide; and combinations thereof. Alternatively, inorganic fillers are exemplified by aluminum oxide, zinc oxide, and combinations thereof. Meltable fillers may comprise Bi, Ga, In, Sn, or an alloy thereof. The meltable filler may optionally further comprise Ag, Au, Cd, Cu, Pb, Sb, Zn, or a combination thereof. Examples of suitable meltable fillers include Ga, In—Bi—Sn alloys, Sn—In—Zn alloys, Sn—In—Ag alloys, Sn—Ag—Bi alloys, Sn—Bi—Cu—Ag alloys, Sn—Ag—Cu—Sb alloys, Sn—Ag—Cu alloys, Sn—Ag alloys, Sn—Ag—Cu—Zn alloys, and combinations thereof. The meltable filler may have a melting point ranging from 50° C. to 250° C., alternatively 150° C. to 225° C. The meltable filler may be a eutectic alloy, a non-eutectic alloy, or a pure metal. Meltable fillers are commercially available.

For example, meltable fillers may be obtained from Indium Corporation of America, Utica, N.Y., U.S.A.; Arconium, Providence, R.I., U.S.A.; and AIM Solder, Cranston, R.I., U.S.A. Aluminum fillers are commercially available, for example, from Toyal America, Inc. of Naperville, Ill., U.S.A. and Valimet Inc., of Stockton, Calif., U.S.A. Silver filler is commercially available from Metalor Technologies U.S.A. Corp. of Attleboro, Mass., U.S.A. Silver flake filler is sold under the tradename RA-127 by the American Chemet Corporation, Chicago, Ill.

Thermally conductive fillers are known in the art and commercially available, see for example, U.S. Pat. No. 6,169,142 (col. 4, lines 7-33). For example, CB-A20S and Al-43-Me are aluminum oxide fillers of differing particle sizes commercially available from Showa-Denko, DAW-45 is aluminum oxide filler commercially available from Denka, and AA-04, AA-2, and AA18 are aluminum oxide fillers commercially available from Sumitomo Chemical Company. Zinc oxides, such as zinc oxides having trademarks KADOX® and XX®, are commercially available from Zinc Corporation of America of Monaca, Pa., U.S.A.

The shape of thermally conductive filler particles is not specifically restricted, however, rounded or spherical particles may prevent viscosity increase to an undesirable level upon high loading of thermally conductive filler in the composition.

Thermally conductive filler may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property such as particle shape, average particle size, particle size distribution, and type of filler. For example, it may be desirable to use a combination of inorganic fillers, such as a first aluminum oxide having a larger average particle size and a second aluminum oxide having a smaller average particle size. Alternatively, it may be desirable, for example, use a combination of an aluminum oxide having a larger average particle size with a zinc oxide having a smaller average particle size. Alternatively, it may be desirable to use combinations of metallic fillers, such as a first aluminum having a larger average particle size and a second aluminum having a smaller average particle size. Alternatively, it may be desirable to use combinations of metallic and inorganic fillers, such as a combination of aluminum and aluminum oxide fillers; a combination of aluminum and zinc oxide fillers; or a combination of aluminum, aluminum oxide, and zinc oxide fillers. Use of a first filler having a larger average particle size and a second filler having a smaller average particle size than the first filler may improve packing efficiency, may reduce viscosity, and may enhance heat transfer.

The average particle size of thermally conductive filler will depend on various factors including the type of thermally conductive filler selected and the exact amount added to the curable silicone composition, as well as the bondline thickness of the device in which the cured product of the composition will be used when the cured product will be used as a thermal interface material (TIM). However, thermally conductive filler may have an average particle size ranging from 0.1 micrometer to 80 micrometers, alternatively 0.1 micrometer to 50 micrometers, and alternatively 0.1 micrometer to 10 micrometers.

The amount of thermally conductive filler as a part of (III) in thermally conductive thermal radical cure silicone composition depends on various factors including the cure mechanism selected and the specific thermally conductive filler selected. However, the amount of thermally conductive filler as a part of (III) may range from 30 vol % to 80 vol %, alternatively 50 vol % to 75 vol % by volume of thermally conductive thermal radical cure silicone composition. Without wishing to be bound by theory, it is thought that when the amount of thermally conductive filler as a part of (III) is greater than 80 vol %, thermally conductive thermal radical cure silicone composition may crosslink to form a cured silicone with insufficient dimensional integrity for some applications, and when the amount of thermally conductive filler as a part of (III) is less than 30%, the cured silicone prepared from thermally conductive thermal radical cure silicone composition may have insufficient thermal conductivity for TIM applications.

When alumina powder is used as thermally conductive filler, it is preferably a mixture of a first spherical alumina filler and a second spherical or irregularly shaped alumina powder having a different, preferably smaller average particle size. The amount of thermally conductive filler (III) is typically added in an amount such that thermally conductive thermal radical cure silicone composition has a thermal conductivity of about 1 Watt per meter Kelvin or more. This improves packing efficiency and can reduce the viscosity and enhance heat transfer.

In certain embodiments, thermally conductive thermal radical cure silicone composition may optionally further comprise a reinforcing filler, which when present may be added in an amount ranging from 0.1% to 95%, alternatively 1% to 60%, based on the weight of all components in the thermally conductive thermal radical cure silicone composition. The exact amount of the reinforcing filler depends on various factors including the form of the cured product of the composition (e.g., gel or rubber) and whether any other fillers are added. Examples of suitable reinforcing fillers include chopped fiber such as chopped KEVLAR®, and/or reinforcing silica fillers such as fume silica, silica aerogel, silica xerogel, and precipitated silica. Fumed silicas are known in the art and commercially available; e.g., fumed silica sold under the name CAB-O-SIL by Cabot Corporation of Massachusetts, U.S.A.

The thermally conductive thermal radical cure silicone composition may optionally further comprise an extending filler in an amount ranging from 0.1% to 95%, alternatively 1% to 60%, and alternatively 1% to 20%, based on the weight of all components in the thermally conductive thermal radical cure silicone composition. Examples of extending fillers include crushed quartz, aluminum oxide, magnesium oxide, calcium carbonate such as precipitated calcium carbonate, zinc oxide, talc, diatomaceous earth, iron oxide, clays, mica, titanium dioxide, zirconia, sand, carbon black, graphite, or a combination thereof. Extending fillers are known in the art and commercially available; such as ground silica sold under the name MIN-U-SIL by U.S. Silica of Berkeley Springs, W. Va. Suitable precipitated calcium carbonates included Winnofil® SPM from Solvay and Ultrapflex® and Ultrapflex® 100 from SMI.

The filler (III) may also include a filler treating agent (III′). The filler treating agent (III′) may be a treating agent, which is known in the art. The amount of filler treating agent (III′) may vary depending on various factors including the type and amounts of thermally conductive fillers selected for component (III) and whether the filler (III) is treated with filler treating agent in situ or pretreated before being combined. However, the components may comprise an amount ranging from 0.1% to 5% of filler treating agent (III′), based on the weight of the filler (III) and the type of the filler.

The filler treating agent (III′) may comprise a silane such as an alkoxysilane, an alkoxy-functional oligosiloxane, a cyclic polyorganosiloxane, a hydroxyl-functional oligosiloxane such as a dimethyl siloxane or methyl phenyl siloxane, a stearate, or a fatty acid. The alkoxysilane may have the formula: R¹⁰ _(p)Si(OR¹¹)_((4-p)), where subscript p is 1, 2, or 3; alternatively p is 3. Each R¹⁰ is independently a monovalent organic group of 1 to 50 carbon atoms, such as a monovalent hydrocarbon group of 1 to 50 carbon atoms, alternatively 6 to 18 carbon atoms. Suitable monovalent hydrocarbon groups for R¹⁰ are exemplified by alkyl groups such as hexyl, octyl, dodecyl, tetradecyl, hexadecyl, and octadecyl; and aromatic groups such as benzyl, phenyl and phenylethyl. R¹⁰ can be a monovalent hydrocarbon group that is saturated or unsaturated and branched or unbranched. Alternatively, R¹⁰ can be a saturated, unbranched, monovalent hydrocarbon group. Each R¹¹ may be a saturated hydrocarbon group of 1 to 4 carbon atoms, alternatively 1 to 2 carbon atoms.

Alkoxysilane filler treating agents are exemplified by hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, phenyltrimethoxysilane, phenylethyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, and a combination thereof.

Alkoxy-functional oligosiloxanes can also be used as filler treating agents. Alkoxy-functional oligosiloxanes and methods for their preparation are known in the art, see for example, EP 1 101 767 A2. For example, suitable alkoxy-functional oligosiloxanes include those of the formula (R¹⁴O)_(q)Si(OSiR¹² ₂R¹³)_((4-q)). In this formula, subscript q is 1, 2, or 3, alternatively q is 3. Each R¹² can be independently selected from saturated and unsaturated monovalent hydrocarbon groups of 1 to 10 carbon atoms. Each R¹³ can be a saturated or unsaturated monovalent hydrocarbon group having at least 11 carbon atoms. Each R14 can be an alkyl group.

Alternatively, alkoxysilanes may be used, but typically in combination with silazanes, which catalyze the less reactive alkoxysilane reaction with surface hydroxyls. Such reactions are typically performed above 100° C. with high shear with the removal of volatile by-products such as ammonia, methanol and water.

Alternatively, the filler treating agent (III′) can be any of the organosilicon compounds typically used to treat silica fillers. Examples of organosilicon compounds include, but are not limited to, organochlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, and trimethyl monochlorosilane; organosiloxanes such as hydroxy-endblocked dimethylsiloxane oligomer, hexamethyldisiloxane, and tetramethyldivinyldisiloxane; organosilazanes such as hexamethyldisilazane and hexamethylcyclotrisilazane; and organoalkoxysilanes such as methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane. Examples of stearates include calcium stearate. Examples of fatty acids include stearic acid, oleic acid, palmitic acid, tallow, coconut oil, and combinations thereof. Examples of filler treating agents and methods for their use are disclosed in, for example, EP 1 101 167 A2 and U.S. Pat. Nos. 5,051,455, 5,053,442, and 6,169,142 (col. 4, line 42 to col. 5, line 2).

Filler treating agents (III′) may include alkoxysilyl functional alkylmethyl polysiloxanes (e.g., partial hydrolysis condensate of R²² _(w)R²³ _(x)Si(OR²⁴)_((4-w-x)) or cohydrolysis condensates or mixtures), or similar materials where the hydrolyzable group may comprise silazane, acyloxy or oximo. In all of these, a group tethered to Si, such as R²² in the formula above, is a long chain unsaturated monovalent hydrocarbon or monovalent aromatic-functional hydrocarbon. Each R²³ is independently a monovalent hydrocarbon group, and each R²⁴ is independently a monovalent hydrocarbon group of 1 to 4 carbon atoms. In the formula above, subscript w is 1, 2, or 3 and subscript x is 0, 1, or 2, with the proviso that the sum (w+x) is 1, 2, or 3. One skilled in the art would recognize that the alkoxysilanes and mercapto-functional compounds described as adhesion promoters for component (IX)(see below) may alternatively be used, in addition to or instead of, filler treating agents (III′) for the filler (III). One skilled in the art could optimize a specific treatment to aid dispersion of the filler without undue experimentation.

When thermally conductive filler of the filler (III) is a metal particle in the form of flakes, the surface of the particles may be coated with a lubricant such as a fatty acid or a fatty acid ester. Such lubricants are typically introduced during the milling process used to produce the metal flakes from a metal powder to prevent the powder from cold welding or forming large agglomerates. Even when the flakes are washed with a solvent after milling, some lubricant may remain chemisorbed on the surface of the metal.

Thermally conductive filler of the filler (III) can also be prepared by treating the surfaces of the metal particles. Some suitable organosilicon compounds that can be used to treat surfaces of the metal particles include compounds typically used to treat silica fillers such as organochlorosilanes, organosiloxanes, organodisilazanes, and organoalkoxysilanes. Other suitable compounds that can be used to treat the surfaces of the metal particles include alkylthiols, fatty acids, titanates, titanate coupling agents, zirconate coupling agents, and combinations thereof.

Other filler treating agents (III′) include alkenyl functional polyorganosiloxanes. Suitable alkenyl functional polyorganosiloxanes include, but are not limited to:

where subscript q has a value up to 1,500. Other treating agents include mono-endcapped alkoxy functional polydiorganosiloxanes, i.e., polydiorganosiloxanes having an alkoxy group at one end. Such treating agents are exemplified by the formula: R²⁵R²⁶ ₂SiO(R²⁶ ₂SiO)_(u)Si(OR²⁷)₃, where subscript u has a value of 0 to 100, alternatively 1 to 50, alternatively 1 to 10, and alternatively 3 to 6. Each R²⁵ is independently selected from an alkyl group, such as Me, Et, Pr, Bu, hexyl, and octyl; and an alkenyl group, such as Vi, allyl, butenyl, and hexenyl. Each R²⁶ is independently an alkyl group such as Me, Et, Pr, Bu, hexyl, and octyl. Each R²⁷ is independently an alkyl group such as Me, Et, Pr, and Bu. Alternatively, each R²⁵, each R²⁶, and each R²⁷ is Me. Alternatively, each R²⁵ is a vinyl group (Vi). Alternatively, each R26 and each R27 is methyl (Me).

Alternatively, a polyorganosiloxane capable of hydrogen bonding is useful as a filler treating agent (III′). This strategy to treating the surface of a thermally conductive filler takes advantage of multiple hydrogen bonds, either clustered or dispersed or both, as the means to tether the compatibilization moiety to the filler surface. The polyorganosiloxane capable of hydrogen bonding has an average, per molecule, of at least one silicon-bonded group capable of hydrogen bonding. The group may be selected from: an organic group having multiple hydroxyl functionalities or an organic group having at least one amino functional group. The polyorganosiloxane capable of hydrogen bonding means that hydrogen bonding is the primary mode of attachment for the polyorganosiloxane to thermally conductive filler. The polyorganosiloxane may be incapable of forming covalent bonds with thermally conductive filler. The polyorganosiloxane capable of hydrogen bonding may be selected from the group consisting of a saccharide-siloxane polymer, an amino-functional polyorganosiloxane, and a combination thereof. Alternatively, the polyorganosiloxane capable of hydrogen bonding may be a saccharide-siloxane polymer.

Component (IV) is a radical initiator. The radical initiator may be a thermal radical initiator. Thermal radical initiators include, but are not limited to, dicumyl peroxide, n-butyl 4,4′-bis(butylperoxy)valerate, 1,1-bis(t-butylperoxy)-3,3,5 trimethyl cyclohexane, di-t-butyl peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane, 1,1-bis(tert-amylperoxy)cyclohexane (Luperox® 531M80); 2,2-bis(tert-butylperoxy)butane; 2,4-pentanedione peroxide (Luperox®224), 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (Luperox® 101), 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne; 2-butanone peroxide, benzoyl peroxide, cumene hydroperoxide, di-tert-amyl peroxide (Luperox® DTA®), lauroyl peroxide (Luperox® LP), tert-butyl hydroperoxide; tert-butyl peracetate; tert-butyl peroxybenzoate; tert-butylperoxy 2-ethylhexyl carbonate; di(2,4-dichlorobenzoyl) peroxide; dichlorobenzoylperoxide (available as Varox® DCBP from R. T. Vanderbilt Company, Inc. of Norwalk, Conn., USA); di(tert-butylperoxyisopropyl)benzene, di(4-methylbenzoyl) peroxide, butyl 4,4-di(tert-butylperoxy)valerate, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane; tert-butyl peroxy-3,5,5-trimethylhexanoate; tert-butyl cumyl peroxide; di(4-tert-butylcyclohexyl) peroxydicarbonate (available as Perkadox 16); dicetyl peroxydicarbonate; dimyristyl peroxydicarbonate; 2,3-dimethyl-2,3-diphenylbutane, dioctanoyl peroxide; tert-butylperoxy 2-ethylhexyl carbonate; tert-amyl peroxy-2-ethylhexanoate, tert-amyl peroxypivalate; and combinations thereof.

Examples of such thermal radical initiators are commercially available under the following trade names: Luperox® sold by Arkema, Inc. of Philadelphia, Pa., U.S.A.; Trigonox and Perkadox sold by Akzo Nobel Polymer Chemicals LLC of Chicago, Ill., U.S.A., VAZO sold by E.I. duPont deNemours and Co. of Wilmington, Del., USA; VAROX® sold by R.T. Vanderbilt Company, Inc. of Norwalk, Conn., U.S.A.; and Norox sold by Syrgis Performance Initiators, Inc. of Helena, Ark., U.S.A.

Alternatively, the radical initiator may comprise a redox reagent as an initiator for radical polymerization. The reagent may be a combination of a peroxide and an amine or a transition metal chelate. The redox reagent is exemplified by, but not limited to, diacyl peroxides such as benzoyl peroxide and acetyl peroxide; hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; dialkyl peroxides such as dicumyl peroxide and ti-t-butyl peroxide; peroxy esters such as t-butyl peroxy acetate; and combinations of thioglycerol and pyrazoles and/or pyrazolones. Alternatively, the redox reagent may be exemplified by dimethylaniline, 3,5-dimethylpyrazole, thioglycerol; and combinations thereof. Examples of suitable redox reagent initiators are known in the art and are exemplified as in U.S. Pat. No. 5,459,206. Other suitable peroxides are known in the art and are commercially available such as lauroyl peroxide (Luperox® LP from Arkema), dichlorobenzoylperoxide (Varox® DCBP from R. T. Vanderbilt Company, Inc.) and 6N tert-butyl hydroperoxide.

The concentration of the radical initiator (IV) may range from 0.01% to 15%, alternatively from 0.1% to 5%, and alternatively 0.1% to 2%, based on the weight of the clustered functional polyorganosiloxane (I).

Thermally conductive thermally radical cure silicone composition may optionally comprise one or more additional components. The additional components are exemplified by (V) a moisture cure initiator, (VI) a crosslinker, (VII) a moisture cure polymer, (VIII) a solvent, (IX) an adhesion promoter, (X) a colorant, (XI) a reactive diluent, (XII) a corrosion inhibitor, (XIII) a polymerization inhibitor, and (XIV) an acid acceptor, and a combination thereof.

Component (V) is a moisture cure initiator (i.e, a condensation reaction catalyst). Examples of condensation reaction catalysts are known in the art and are disclosed in U.S. Pat. Nos. 4,962,076; 5,051,455; 5,053,442; 4,753,977 at col. 4, line 35 to col. 5, line 57; and U.S. Pat. No. 4,143,088 at col. 7, line 15 to col. 10, line 35. The amount of the condensation reaction catalyst depends on various factors including the type of catalyst selected and the choice of the remaining components in the composition, however the amount of the condensation reaction catalyst may range from 0.001% to 5% based on the weight of thermally conductive thermally radical cure silicone composition.

Suitable condensation reaction catalyst may be a Lewis acid; a primary, secondary, or tertiary organic amine; a metal oxide; a titanium compound; a tin compound; a zirconium compound; or a combination thereof. The condensation reaction catalyst may comprise a carboxylic acid salt of a metal ranging from lead to manganese inclusive in the electromotive series of metals. Alternatively, the condensation reaction catalyst may comprise a chelated titanium compound, a titanate such as a tetraalkoxytitanate, a titanium ester, or a combination thereof. Examples of suitable titanium compounds include, but are not limited to, diisopropoxytitanium bis(ethylacetoacetate), tetrabutoxy titanate, tetrabutyltitanate, tetraisopropyltitanate, and bis-(ethoxyacetoacetonate)diisopropoxy titanium (IV), and a combination thereof. Alternatively the condensation reaction catalyst may comprise a tin compound such as dibutyltin diacetate; dibutyltin dilaurate; dibutyl tin oxide; stannous octoate; tin oxide; a titanium ester, such as tetrabutyl titanate, tetraethylhexyl titanate and tetraphenyltitanate; a siloxytitanate, such as tetrakis(trimethylsiloxy)titanium and bis(trimethylsiloxy)-bis(isopropoxy)titanium; and a betadicarbonyltitanium compound, such as bis(acetylacetonyl)diisopropyl titanate; or a combination thereof. Alternatively, the condensation reaction catalyst may comprise an amine, such as hexylamine; or an acetate or quat salt of an amine.

Component (VI) is a crosslinker. The type and amount of crosslinker will depend on various factors including the type and amount of curable groups on component (VII).

In certain embodiments, the crosslinker (VI) is a condensation reaction crosslinker that may be selected from, for example, trialkoxysilanes exemplified by propyltrimethoxysilane, phenyltrimethoxysilane, glycidoxypropyltrimethoxysilane, ethyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, methyltrimethoxysilane, phenyl trimethoxysilane, and methyltriethoxysilane; acetoxysilanes such as methyltriacetoxysilane or ethyltriacetoxysilane; ketoximosilanes such as methyltri(methylethylketoximo) silane, tetra(methylethylketoximo)silane, methyltris(methylethylketoximo) silane, and vinyltris(methylethylketoximo) silane; alkyl orthosilicates such as tetraethyl orthosilicate, tetramethoxysilane, tetraethoxysilane, and condensation products of these orthosilicates, which are typically referred to as alkyl polysilicates; methylvinyl bis(n-methylacetamido) silane; and a combination thereof.

In certain embodiments, the amount of crosslinker (VI) utilized in the silicone silicone composition is dependent upon numerous factors, but is based primarily upon the type and amount of curable groups contained in components (I) and (II). In certain embodiments, the amount of crosslinker is from 0.1 to 50 weight percent, such as from 0.5 to 30 weight percent, based upon the total weight of component (VII).

Component (VII) is a moisture cure polymer that comprises an organopolysiloxane polymer of the formula: (OR⁷)_(3-z)R⁶ _(z)Si-Q-(R²⁵ ₂SiO_(2/2))_(y)-Q-SiR⁶ _(z)(OR⁷)_(3-z), wherein each R²⁵ is independently a monovalent hydrocarbon radical having 1 to 6 carbon atoms, each R⁶ independently is a monovalent hydrocarbon radical having 1 to 6 carbon atoms, each R⁷ independently is selected from the group consisting of an alkyl radical and alkoxyalkyl radical, Q is a divalent linking radical, the subscript z has a value of 0, 1 or 2, and the subscript y has a value of 60 to 1000.

In certain embodiments, the moisture cure polymer (VI) is present in an amount ranging from 0.1 to 5 weight percent based on the weight of thermally conductive thermally radical cure silicone composition.

The Q radical is a divalent linking radical linking the silicon atom of the curing radical to a silicon atom of the resin. Q is typically selected from the types of divalent radicals that are used to link silicon atoms in a hydrolytically stable manner and include, but are not limited to, hydrocarbons such as alkylene, for example ethylene, propylene, and isobutylene and phenylene; siloxanes such as, for example, polydimethylsiloxane; and combinations thereof. Preferably, the number of hydrocarbon radical units in the Q divalent linking radical numbers from 2 to 12, alternatively 2, and the number of siloxane radical units in the Q divalent linking radical numbers from 0 to 20, alternatively 2.

Component (VIII) is a solvent. Suitable solvents are exemplified by organic solvents such as toluene, xylene, acetone, methylethylketone, methyl isobutyl ketone, hexane, heptane, alcohols such as decyl alcohol or undecyl alcohol, and a combination thereof; and non-crosslinkable silicone solvents such as trimethylsiloxy-terminated polydimethylsiloxanes, trimethylsiloxy-terminated polymethylphenylsiloxanes, and a combination thereof. Examples of silicone solvents are known in the art and are commercially available, for example, as Dow Corning® OS Fluids from Dow Corning Corporation of Midland, Mich., U.S.A. The amount of component (VIII) may range from 0.001% to 90% based on the weight of thermally conductive thermally radical cure silicone composition.

Component (IX) is an adhesion promoter. Examples of suitable adhesion promoters include an alkoxysilane such as an epoxy-functional alkoxysilane, or a mercapto-functional compound; a combination of an alkoxysilane and a hydroxy-functional polyorganosiloxane; a mercapto-functional compound; an unsaturated compound; an epoxy-functional silane; an epoxy-functional siloxane; a combination, such as a reaction product, of an epoxy-functional silane or epoxy-functional siloxane and a hydroxy-functional polyorganosiloxane; or a combination thereof. Suitable adhesion promoters are known in the art and are commercially available. For example, Silquest® A186 is beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane which is commercially available from Crompton OSi Specialties of Middlebury, Conn., USA. CD9050 is a monofunctional acid ester useful as an adhesion promoter that provides adhesion to metal substrates and is designed for radiation curable compositions. CD9050 is commercially available from Sartomer Co. SR489D is tridecyl acrylate, SR395 is isodecyl acrylate, SR257 is stearyl acrylate, SR506 is isobornyl acrylate, SR833S is tricyclodecane dimethanol diacrylate, SR238 is 1,6 hexanediol diacrylate, and SR351 is trimethylol propane triacrylate, all of which are also commercially available from Sartomer Co. The amount of adhesion promoter (IX) added to the composition depends on various factors including the specific adhesion promoter selected, the other components of the composition, and the end use of the composition, however, the amount may range from 0.01% to 5% based on the weight of thermally conductive thermally radical cure silicone composition. Other suitable adhesion promoters, which are useful to promote adhesion to metals, include maleic anhydride, methacrylic anhydride, and glycidyl methacrylate.

Component (IX) can be an unsaturated or epoxy-functional compound. Suitable epoxy-functional compounds are known in the art and commercially available, see for example, U.S. Pat. Nos. 4,087,585; 5,194,649; 5,248,715; and 5,744,507 (at col. 4-5). Component (g) may comprise an unsaturated or epoxy-functional alkoxysilane. For example, the functional alkoxysilane can have the formula R²⁰ _(v)Si(OR²¹)_((4-v)), where subscript v is 1, 2, or 3, alternatively v is 1.

Each R²⁰ is independently a monovalent organic group with the proviso that at least one R²⁰ is an unsaturated organic group or an epoxy-functional organic group. Epoxy-functional organic groups for R²⁰ are exemplified by 3-glycidoxypropyl and (epoxycyclohexyl)ethyl. Unsaturated organic groups for R²⁰ are exemplified by 3-methacryloyloxypropyl, 3-acryloyloxypropyl, and unsaturated monovalent hydrocarbon groups such as vinyl, allyl, hexenyl, undecylenyl.

Each R²¹ is independently an unsubstituted, saturated hydrocarbon group of 1 to 4 carbon atoms, alternatively 1 to 2 carbon atoms. R²¹ is exemplified by methyl, ethyl, propyl, and butyl.

Examples of suitable epoxy-functional alkoxysilanes include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (epoxycyclohexyl)ethyldimethoxysilane, (epoxycyclohexyl)ethyldiethoxysilane and combinations thereof. Examples of suitable unsaturated alkoxysilanes include vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, hexenyltrimethoxysilane, undecylenyltrimethoxysilane, 3-methacryloyloxypropyl trimethoxysilane, 3-methacryloyloxypropyl triethoxysilane, 3-acryloyloxypropyl trimethoxysilane, 3-acryloyloxypropyl triethoxysilane, and combinations thereof. Alternatively, examples of suitable adhesion promoters include glycidoxypropyltrimethoxysilane and a combination of glycidoxypropyltrimethoxysilane with an aluminum chelate or zirconium chelate.

Component (IX) may comprise an epoxy-functional siloxane such as a reaction product of a hydroxy-terminated polyorganosiloxane with an epoxy-functional alkoxysilane, as described above, or a physical blend of the hydroxy-terminated polyorganosiloxane with the epoxy-functional alkoxysilane. Component (IX) may comprise a combination of an epoxy-functional alkoxysilane and an epoxy-functional siloxane. For example, component (VII) is exemplified by a mixture of 3-glycidoxypropyltrimethoxysilane and a reaction product of hydroxy-terminated methylvinylsiloxane with 3-glycidoxypropyltrimethoxysilane, or a mixture of 3-glycidoxypropyltrimethoxysilane and a hydroxy-terminated methylvinylsiloxane, or a mixture of 3-glycidoxypropyltrimethoxysilane and a hydroxy-terminated methylvinyl/dimethylsiloxane copolymer. When used as a physical blend rather than as a reaction product, these components may be stored separately in multiple-part kits.

Suitable mercapto-functional compounds include an organomercaptan, a mercapto containing silane, or a combination thereof. Suitable mercapto containing silanes include 3-mercaptopropyltrimethoxysilane. Suitable mercapto-functional compounds are disclosed in U.S. Pat. No. 4,962,076. One skilled in the art would recognize that certain components described herein may be added to the composition for more than one or different purposes. For example, alkoxysilanes may be use as adhesion promoters, filler treating agents, and/or as crosslinking agents in condensation reaction curable silicone compositions.

Component (X) is a colorant (e.g., dye or pigment). Examples of suitable colorants include carbon black, Stan-Tone 40SP03 Blue (which is commercially available from PolyOne) and Colorant BA 33 Iron Oxide pigment (which is commercially available from Cathay Pigments (USA), Inc. Valparaiso, Ind. 46383 USA). Examples of colorants are known in the art and are disclosed in U.S. Pat. Nos. 4,962,076; 5,051,455; and 5,053,442. The amount of colorant added to the curable silicone composition depends on various factors including the other components of the composition, and the type of colorant selected, however, the amount may range from 0.001% to 20% based on the weight of the composition.

Component (XI) is a reactive diluent that is different than the silicone reactive diluent (II). Component (XI) may be diluent that reacts with a functional group on component (I) or (II). The reactive diluent may be a monofunctional reactive diluent, a difunctional reactive diluent, a polyfunctional reactive diluent, or a combination thereof. The reactive diluent (XI) selected will depend on various factors including the curable groups on components (I) and (II). However, examples of suitable reactive diluents include an acrylate, an anhydride such as a maleic anhydride or methacrylic anhydride, an epoxy such as a monofunctional epoxy compound, a methacrylate such as glycidyl methacrylate, an oxetane, a vinyl acetate, a vinyl ester, a vinyl ether, a fluoro alkyl vinyl ether, a vinyl pyrrolidone such as N-vinyl pyrrolidone, a styrene, or a combination thereof.

Mono-functional acrylate and methacrylate esters are commercially available from companies such as Sartomer, Rohm Haas, Hitachi Chemical, Arkema, Inc., Cytec, Sans Ester Corp, Rahn, and Bomar Specialties Co. Specific examples include methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; butyl acrylate; butyl methacrylate; cyclohexyl acrylate; hexyl acrylate; 2-ethylhexyl acrylate; isodecyl methacrylate; isobornyl methacrylate; hydroxyethyl methacrylate; hydroxypropyl acrylate; hydroxypropyl methacrylate; n-octyl acrylate; cyclohexyl methacrylate; hexyl methacrylate; 2-ethylhexyl methacrylate; decyl methacrylate; dodecyl methacrylate; lauryl acrylate; tert-butyl methacrylate; acrylamide; N-methyl acrylamide; diacetone acrylamide; N-tert-butyl acrylamide; N-tert-octyl acrylamide; N-butoxyacrylamide; gamma-methacryloxypropyl trimethoxysilane; dicyclopentadienyloxyethyl methacrylate; 2-cyanoethyl acrylate; 3-cyanopropyl acrylate; tetrahydrofurfuryl methacrylate; tetrahydrofurfuryl acrylate; glycidyl acrylate; acrylic acid; methacrylic acid; itaconic acid; glycidyl methacrylate; 1,12 dodecanediol dimethacrylate; 1,3-butylene glycol diacrylate; 1,3-butylene glycol dimethacrylate; 1,3-butylene glycol dimethacrylate; 1,4-butanediol diacrylate; 1,4-butanediol dimethacrylate; 1,4-butanediol dimethacrylate; 1,6 hexanediol diacrylate; 1,6 hexanediol dimethacrylate; alkoxylated cyclohexane dimethanol diacrylate; alkoxylated hexanediol diacrylate; alkoxylated neopentyl glycol diacrylate; cyclohexane dimethanol diacrylate; cyclohexane dimethanol dimethacrylate; diethylene glycol diacrylate; diethylene glycol dimethacrylate; dipropylene glycol diacrylate; ethoxylated bisphenol a diacrylate; ethoxylated bisphenol a dimethacrylate; ethylene glycol dimethacrylate; neopentyl glycol diacrylate; neopentyl glycol dimethacrylate; polypropylene glycoldimethacrylate; propoxylated neopentyl glycol diacrylate; propoxylated neopentyl glycol diacrylate; tricyclodecane dimethanol diacrylate; triethylene glycol diacrylate; trimethylolpropane triacrylate; trimethylolpropane trimethacrylate; tris(2-hydroxy ethyl) isocyanurate triacrylate; tris(2-hydroxy ethyl) isocyanurate triacrylate; n,n′-m-phenylenedimaleimide; triallyl cyanurate; triallyl isocyanurate; metallic diacrylate; metallic dimethacrylate; metallic monomethacrylate; metallic diacrylate (difunctional); metallic dimethacrylate (difunctional); triethoxysilylpropyl methacrylate; tributoxysilylpropyl methacrylate; dimethoxymethylsilylpropyl methacrylate; diethoxymethylsilylpropyl methacrylate; dibutoxymethylsilylpropyl methacrylate; diisopropoxymethylsilylpropyl methacrylate; dimethoxysilylpropyl methacrylate; diethoxysilylpropyl methacrylate; dibutoxysilylpropyl methacrylate; diisopropoxysilylpropyl methacrylate; trimethoxysilylpropyl acrylate; triethoxysilylpropyl acrylate; tributoxysilylpropyl acrylate; dimethoxymethylsilylpropyl acrylate; diethoxymethylsilylpropyl acrylate; dibutoxymethylsilylpropyl acrylate; diisopropoxymethylsilylpropyl acrylate; dimethoxysilylpropyl acrylate; diethoxysilylpropyl acrylate; dibutoxysilylpropyl acrylate; and diisopropoxysilylpropyl acrylate.

Examples of suitable vinyl ethers include, but are not limited to butanediol divinyl ether, cyclohexanedimethanol divinyl ether, cyclohexanedimethanol monovinyl ether, cyclohexyl vinyl ether, diethyleneglycol divinyl ether, diethyleneglycol monovinyl ether, dodecyl vinyl ether, ethyl vinyl ether, hydroxybutyl vinyl ether, isobutyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, n-propyl vinyl ether, octadecyl vinyl ether, triethyleneglycol divinyl ether, and combinations thereof. Vinyl ethers are known in the art and commercially available from BASF AG of Germany, Europe. The amount of component (IX) depends on various factors such as the specific reactive diluent selected, but the amount may range from 0.01 to 10% based on the weight of thermally conductive thermally radical cure silicone composition. One skilled in the art would recognize that some of the reactive diluents described herein (such as the difunctional and polyfunctional acrylates and methacrylates) may also be used in addition to, or instead of, the reactive species described above as component c) of (I).

Component (XII) is a corrosion inhibitor. Examples of suitable corrosion inhibitors include benzotriazole, mercaptabenzotriazole, mercaptobenzothiazole, and commercially available corrosion inhibitors such as 2,5-dimercapto-1,3,4-thiadiazole derivative (CUVAN® 826) and alkylthiadiazole (CUVAN® 484) from R. T. Vanderbilt. The amount of component (XII) may range from 0.05% to 0.5% based on the weight of thermally conductive thermally radical cure silicone composition.

Component (XIII) is a polymerization inhibitor. Examples of suitable polymerization inhibitors for acrylate and methacrylate curable groups include, but are not limited to: 2,6,-Di-tert-butyl-4-(dimethylaminomethyl)phenol (DBAP), hydroquinone (HQ); 4-methoxyphenol (MEHQ); 4-ethoxyphenol; 4-propoxyphenol; 4-butoxyphenol; 4-heptoxyphenol; butylated hydroxytoluene (BHT); hydroquinone monobenzylether; 1,2-dihydroxybenzene; 2-methoxyphenol; 2,5-dichlorohydroquinone; 2,5-di-tert-butylhydroquinone; 2-acetylhydroquinone; hydroquinone monobenzoate; 1,4-dimercaptobenzene; 1,2-dimercaptobenzene; 2,3,5-trimethylhydroquinone; 4-aminophenol; 2-aminophenol; 2-N, N-dimethylaminophenol; 2-mercaptophenol; 4-mercaptophenol; catechol monobutylether; 4-ethylaminophenol; 2,3-dihydroxyacetophenone; pyrogallol-1,2-dimethylether; 2-methylthiophenol; t-butyl catechol; di-tert-butylnitroxide; di-tert-amylnitroxide; 2,2,6,6-tetramethyl-piperidinyloxy; 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy; 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy; 4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy; 4-amino-2,2,6,6-tetramethyl-piperidinyloxy; 4-ethanoloxy-2,2,6,6-tetramethyl-piperidinyloxy; 2,2,5,5-tetramethyl-pyrrolidinyloxy; 3-amino-2,2,5,5-tetramethyl-pyrrolidinyloxy; 2,2,5,5-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy; 2,2,5,5-tetramethyl-3-pyrrolinyl-1-oxy-3-carboxylic acid; 2,2,3,3,5,5,6,6-octamethyl-1,4-diazacyclohexyl-1,4-dioxy; salts of 4-nitrosophenolate; 2-nitrosophenol; 4-nitrosophenol; copper dimethyldithiocarbamate; copper diethyldithiocarbamate; copper dibutyldithiocarbamate; copper salicylate; methylene blue; iron; phenothiazine (PTZ); 3-oxophenothiazine; 5-oxophenothiazine; phenothiazine dimer; 1,4-benzenediamine; N-(1,4-dimethylpentyl)-N′-phenyl-1,4-benzenediamine; N-(1,3-dimethylbutyl)-N′-phenyl-1,4-benzenediamine; N-nitrosophenylhydroxylamine and salts thereof; nitric oxide; nitrobenzene; p-benzoquinone; pentaerythrityl tetrakis(3-laurylthiopropionate); dilauryl thiodipropionate; distearyll thiodipropionate; ditridecyl thiodipropionate; tetrakis[methylene 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; N,N′-hexamethyl (3,5-di-tertbutyl-4-hydroxyhydrocinnamamide); iso-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; 2,2′-ethylidenebis-(4,6-di-tert-butylphenol); 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; 4,6-bis(octylthiomethyl)-o-cresol; triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate; tris-(3,5-di-tert-butylhydroxybenzyl) isocyanurate; tris(2,4-di-tert-butylphenyl) phosphate; distearyl pentaerythritol diphosphite; bis(2,4-di-tert-butyl phenyl)pentaerythritol diphosphite; 2,5-di-tert-amyl-hydroquinone; or isomers thereof; combinations of two or more thereof; or combinations of one or more of the above with molecular oxygen. When present, the polymerization inhibitor may be added to the curable silicone composition in an amount ranging from 100 ppm to 4,000 ppm. Polymerization inhibitors are known in the art and are disclosed, for example in EP 1 359 137.

Component (XIV) is an acid acceptor. The acid acceptor may comprise a metal oxide such as magnesium oxide. Acid acceptors are known in the art and are commercially available under tradenames including Rhenofit F, Star Mag CX-50, Star Mag CX-150, BLP-3, and MaxOx98LR. Rhenofit F was calcium oxide from Rhein Chemie Corporation of Chardon, Ohio, USA. Star Mag CX-50 was magnesium oxide from Merrand International Corp. of Portsmouth, N.H., USA. MagOX 98LR was magnesium oxide from Premier Chemicals LLC of W. Conshohocken, Pa., USA. BLP-3 was calcium carbonate was Omya Americas of Cincinnati, Ohio, USA.

The thermally conductive thermal radical cure silicone compositions of the present invention, as noted above, are preferably formed in a method known the “Premade Polymer Route”. In the first method in accordance with a first embodiment, the thermally conductive thermal radical cure silicone compositions is formed comprising (I) a clustered functional polyorganopolysiloxane; (II) a silicone reactive diluent; (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator. In the second embodiment, wherein a higher viscosity thermally conductive thermal radical cure silicone composition is desired, the thermally conductive thermal radical cure silicone compositions is formed comprising (I) a clustered functional polyorganopolysiloxane; (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator (i.e., it does not include the silicone reactive diluent (II)). Each embodiment is described below.

In the first embodiment, beginning with Step 1, one or both of the clustered functional polyorganosiloxane (I) and the silicone reactive diluent (II) (which are each premade in accordance with any possible embodiment described above) are introduced to a reaction vessel along with the filler (III) that includes a thermally conductive filler and mixed to homogeneity. In certain embodiments, the clustered functional polyorganosiloxane (I) is introduced as a masterbatch comprising a polyorganosiloxane having aliphatically unsaturated organic groups and a treated filler as described above.

The thermally conductive filler can be one size or can be the combination of differing particle size and different particle size distribution. In certain embodiments, the majority of thermally conductive filler added in this first step has an average surface area of 0.5 m²/gram or greater (i.e., as defined herein, are larger surface area particles).

Next, in Step 2, the mixture of Step 1 is combined with the filler treating agent (III′), including any one or more of the filler treating agents (III′) described above. The mixture is then mixed to homogeneity. Alternatively, the filler treating agent (III′) may be added to the reaction vessel as a part of Step 1.

In Step 3, the mixture is then heated to a temperature sufficient to insure in situ treating of the thermally conductive fillers with the filler treating agent (III′) in the presence of (I) or (II), or a combination of (I) and (II). The in situ treating reaction may be initiated by raising the temperature of the mixture to 50° C. to 110° C., alternatively 70° C. to 85° C. Preferably, Step 3 is performed under a vacuum.

In Optional Step 4, the reaction mixture of Step 3 is preferably cooled to a temperature below 50° C. for ease of handling, wherein additional components comprising the clustered functional polyorganosiloxane (I), the silicone reactive diluent (II), the filler (III), and the filler treating agent (III′), or a combination thereof, are added and mixed to homogeneity.

The additional filler (III) added in Optional Step 4 can include thermally conductive fillers of one size or can be the combination of differing particle size and different particle size distribution and can include larger surface area particles, as described above, or smaller surface area particles (i.e., those having an average surface area of less than 0.5 m²/gram).

In Optional Step 5, the vessel is reheated to a temperature sufficient to insure in situ treating of the additional thermally conductive filler with the additional filler treating agent (III′) in the presence of (I) or (II), or a combination of (I) and (II). The in situ treating reaction may be initiated by raising the temperature to 50° C. to 110° C., alternatively 70° C. to 85° C. Preferably, this step is performed under a vacuum.

Next, in Step 6, Optional Step 4 alone, or Optional Step 4 in combination with Optional Step 5, may be repeated one or more times until the desired amount of thermally conductive filler is loaded into the mixture.

Next, in Step 7, the temperature of the reaction vessel is cooled and each of the additional components (V)-(XIV) described above are blended with the resultant mixture and mixed to homogeneity. In addition, either component (I) or component (II) may be added to insure that the resultant mixture includes both (I) and (II). In certain embodiments, the temperature is cooled to below 30° C. prior to the addition of components (V)-(XIV). In certain embodiments, components (V)-(XIV) are added individually and blended with the resultant mixture, while in other embodiments one or more of the components (V)-(XIV) may be added and the same time and blended.

Finally, in Step 8, at a temperature less than 30° C., the radical inhibitor (IV) is added to the mixture and mixed to homogeneity to form thermally conductive thermal radical cure silicone composition. Alternatively, in certain embodiments, the radical inhibitor (IV) may be added as a part of Step 7 when the temperature of Step 7 is below 30° C.

In the second embodiment, beginning with Step 1, the clustered functional polyorganosiloxane (I) (which is premade in accordance with any possible embodiment described above) is introduced to a reaction vessel along with the filler (III) that includes a thermally conductive filler and mixed to homogeneity. In certain embodiments, the clustered functional polyorganosiloxane (I) is introduced as a masterbatch comprising a polyorganosiloxane having aliphatically unsaturated organic groups and a treated filler as described above.

The thermally conductive filler can be one size or can be the combination of differing particle size and different particle size distribution. In certain embodiments, the majority of thermally conductive filler added in this first step has an average surface area of 0.5 m²/gram or greater (i.e., as defined herein, are larger surface area particles).

Next, in Step 2, the mixture of Step 1 is combined with the filler treating agent (III′), including any one or more of the filler treating agents (III′) described above. The mixture is then mixed to homogeneity. Alternatively, the filler treating agent (III′) may be added to the reaction vessel as a part of Step 1.

In Step 3, the mixture is then heated to a temperature sufficient to insure in situ treating of the thermally conductive fillers with the filler treating agent (III′) in the presence of the clustered functional polyorganosiloxane (I). The in situ treating reaction may be initiated by raising the temperature of the mixture to 50° C. to 110° C., alternatively 70° C. to 85° C. Preferably, Step 3 is performed under a vacuum.

In Optional Step 4, the reaction mixture of Step 3 is preferably cooled to a temperature below 50° C. for ease of handling, wherein additional components comprising the clustered functional polyorganosiloxane (I), the filler (III), and the filler treating agent (III′), or a combination thereof, are added and mixed to homogeneity.

The additional filler (III) added in Optional Step 4 can include thermally conductive fillers of one size or can be the combination of differing particle size and different particle size distribution and can include larger surface area particles, as described above, or smaller surface area particles (i.e., those having an average surface area of less than 0.5 m²/gram).

In Optional Step 5, the vessel is reheated to a temperature sufficient to insure in situ treating of the additional thermally conductive filler with the additional filler treating agent (III′) in the presence of the clustered functional polyorganosiloxane (I). The in situ treating reaction may be initiated by raising the temperature to 50° C. to 110° C., alternatively 70° C. to 85° C. Preferably, this step is performed under a vacuum.

Next, in Step 6, Optional Step 4 alone, or Optional Step 4 in combination with Optional Step 5, may be repeated one or more times until the desired amount of thermally conductive filler is loaded into the mixture.

Next, in Step 7, the temperature of the reaction vessel is cooled and each of the additional components (V)-(XIV) described above are blended with the resultant mixture and mixed to homogeneity. In certain embodiments, the temperature is cooled to below 30° C. prior to the addition of components (V)-(XIV). In certain embodiments, components (V)-(XIV) are added individually and blended with the resultant mixture, while in other embodiments one or more of the components (V)-(XIV) may be added and the same time and blended.

Finally, in Step 8, at a temperature less than 30° C., the radical inhibitor (IV) is added to the mixture and mixed to homogeneity to form thermally conductive thermal radical cure silicone composition. Alternatively, in certain embodiments, the radical inhibitor (IV) may be added as a part of Step 7 when the temperature of Step 7 is below 30° C.

The thermally conductive filler introduced as a part of the filler (III) added at any step during the Premade Polymer Process according to either the first embodiment or the second embodiment can have filler treatments, including alkylthiols such as octadecyl mercaptan and others, and fatty acids such as oleic acid, stearic acid, titanates, titanate coupling agents, zirconate coupling agents, and a combination thereof. Stated another way, the thermally conductive filler introduced at any step during the Premade Polymer Process according to either the first embodiment or the second embodiment is referred to as a “dirty filler”, i.e., a less pure form of thermally conductive fillers that do not include such treatments

The resultant thermally conductive thermal radical cure silicone composition formed by the Premade Polymer Process according to either the first embodiment or the second embodiment achieved a thermal conductivity greater than 0.5 W/mK (watts per meter kelvin), alternatively greater than 1 W/mK, alternatively greater than 1.5 W/mK.

The thermally conductive thermal radical cure silicone composition formed by the Premade Polymer Route as described above, and cured silicone coatings prepared by curing the resultant thermally conductive thermal radical cure silicone composition, are useful in electronics applications, including both microelectronics and macroelectronics applications as well as optoelectronics applications and thermally conductive electronics applications, such as making thermally conductive adhesives. As thermally conductive thermal radical cure silicone compositions of the present invention are cured both thermal radical cure and moisture cure, they may be utilized on a wider variety of substrates than traditional radical cure silicone compositions or moisture cure silicone compositions.

Cured silicone adhesives prepared from such a thermally conductive thermal radical cure silicone composition may adhere to various electronics substrates, including metals such as aluminum, copper, and electroless nickel; as well as polymeric substrates such as FR4, Nylon, polycarbonate, Lucite (which is polymethylmethacrylate, PMMA), polybutylene terephthalate (PBT), and Solvay liquid crystal polymers.

Composite articles according to the invention preferably consist of the aforementioned thermally conductive thermal radical cure silicone compositions, and can be disposed or applied to a single substrate or between multiple substrates. At least one surface of the substrate to which thermally conductive thermal radical cure silicone compositions is applied should have a polymeric or largely inorganic surface. Any additional substrates can be organic, thermoplastic, thermosetting, metal, ceramic, or another suitable inorganic material. The substrate(s) can be multi-layered such as a printed circuit board in which case there is obtained improved adhesion between thermally conductive thermal radical cure silicone compositions and the substrate or substrates of the composite article.

Composite articles are made by bonding thermally conductive thermal radical cure silicone compositions to at least one surface of the substrate in the composite article. This is carried out by curing the composition at temperatures below 150° C., alternatively at 70-100° C., and achieving sufficient adherence such that thermally conductive thermal radical cure silicone composition and the substrate are bonded together securely to form the composite article.

Fully bonded composite articles can be made by disposing thermally conductive thermal radical cure silicone composition onto at least one surface of the polymeric substrate at a temperature less than the boiling point of water (100° C.), and then concurrently curing thermally conductive thermal radical cure silicone compositions and bonding it to the polymeric substrate(s). This obviates the need to pre-dry the substrate(s). Composite articles can also be cured and bonded in a similar fashion at room temperature that eliminates the need to use a curing oven.

Mixing and dispensing of multi-component compositions can be carried out in several ways. For example, the compositions can be mixed at the desired volume ratio in air in a bag or through a pressurized gun. It is beneficial to tailor the viscosity and density of thermally conductive thermal radical cure silicone compositions to allow for their efficient mixing and dispensing. Fillers of varying density and viscosity modifiers such as solvents, monomers, and polymers can be used to impart control of these properties. It is also beneficial to exclude oxygen from the environment in the mixing device before dispensing it on a substrate to minimize pre-mature curing and plugging of the mixing and dispensing device.

Thermally conductive thermal radical cure silicone compositions of the invention are useful for preparing electrically conductive rubbers, electrically conductive tapes, electrically conductive curable adhesives, electrically conductive foams, and electrically conductive pressure sensitive adhesives. Thermally conductive thermal radical cure silicone compositions are especially useful for preparing electrically conductive silicone adhesives. Electrically conductive silicone adhesives have numerous uses including die attach adhesives, solder replacements, and electrically conductive coatings and gaskets. In particular, electrically conductive silicone adhesives are useful for bonding electronic components to flexible or rigid substrates.

Thermally conductive thermal radical cure silicone compositions can also be used for the assembly of electronic components, as substitutes for soldering, as electrical and thermal interface materials, and as conductive inks. Thermally conductive thermal radical cure silicone compositions can be in the form of a rigid part or a flexible elastomer, and can be dispensed, pre-cured in rolls or sheet form as films, such as pressure sensitive adhesives. They can also be dispensed and cured in place in the final application. Foamed thermally conductive thermal radical cure silicone compositions can be used as gaskets and seals in applications such as electrical and electronic housings to prevent the transmission of electromagnetic and radio frequency noise across the sealed areas.

Thermally conductive thermal radical cure silicone compositions are similarly useful for preparing thermally conductive rubbers, thermally conductive tapes, thermally conductive curable adhesives, thermally conductive foams, and thermally conductive pressure sensitive adhesives. Thermally conductive thermal radical cure silicone compositions are especially useful for preparing thermally conductive silicone adhesives. Thermally conductive thermal radical cure silicone compositions have several uses including their use as die attach adhesives, solder replacements, and thermally conductive coatings and gaskets. Thermally conductive thermal radical cure silicone compositions are especially useful for bonding electronic components to flexible or rigid substrates.

Thermally conductive thermal radical cure silicone compositions can also be used for assembling electronic components, as substitutes for soldering, as thermal interface materials, and as thermally conductive inks or greases. Thermally conductive thermal radical cure silicone compositions can be in the form of a rigid part or in the form of a flexible elastomer and can be dispensed, pre-cured in rolls or in sheets as films, such as pressure sensitive adhesives. They can also be displaced and cured in place in the final application. Partially cured thermally conductive thermal radical cure silicone compositions can be used as thermally conductive greases. Foamed thermally conductive thermal radical cure silicone compositions can be used as gaskets and seals in electrical and electronic housings. When thermally conductive thermal radical cure silicone composition is a thermally conductive adhesive, the thermally conductive thermal radical cure adhesive composition offers particular advantages as a thermal interface material to provide good bonding strength between heat sinks, heat spreaders, or heat dissipation devices, particularly where the heat sink or heat dissipation device has a polymeric-matrix.

So that those skilled in the art can understand and appreciate the invention taught herein, the following examples are presented, it being understood that these examples should not be used to limit the scope of this invention found in the claims attached hereto. All parts and percentages in the examples are on a weight basis and all measurements were obtained at 25° C., unless indicated to the contrary.

Comparative Examples

These examples are intended to illustrate the invention to one of ordinary skill in the art and should not be interpreted as limiting the scope of the invention set forth in the claims.

NMR: Solution-state ²⁹Si- and ¹³C-NMR spectra were recorded on a Mercury VX 400 MHz spectrometer at room temperature (20-22° C.) using CDCl3 (Isotec) in a 16 mm Si-free probe. Cr(acac)₃ (Chromium acetylacetonate) (20 mM) was added to NMR samples as a relaxation agent. ²⁹Si NMR spectra were acquired at 79.493 MHz and processed with 5 Hz of Lorentzian line broadening. The spectra were only semiquantitative due to the long relaxation times of the ²⁹Si nucleus, but relative comparison of spectra acquired under identical conditions was considered quantitative. ¹³C NMR spectra were acquired at 100.626 MHz and processed with 3 Hz of Lorentzian line broadening. For both nuclei, 256-512 scans with a 90° pulse width were typically co-added to achieve adequate sensitivity; a 6-second (²⁹Si) or 12-second (13C) delay between pulses was used. Gated decoupling was used to remove negative nuclear Overhauser effects. Chemical shifts were referenced to external tetramethylsilane (TMS).

I. List of Components for Examples:

DOW CORNING® SFD-119; 0.46 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-117; 0.2 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-120; 0.13 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-128; 0.088 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® Q2-50575; 0.15 wt % SiH methylhydrogen silicone, linear;

DOW CORNING® Q2-5565; 0.027 wt % SiH methylhydrogen silicone, linear;

Methylhydrogensiloxane; 1.67 wt % SiH methylhydrogen silicone cyclic;

DOW CORNING® 2-0707; Platinum catalyst 0.52 wt % Platinum;

MB2030-(DOW CORNING® SFD-128/silica blend);

Methyltrimethoxysilane (MTM); DOW CORNING® Z6070;

OFS-1579/ETS900—Mixture of methyl and ethyltriacetoxysilane;

DOW CORNING® Z-6030 SILANE Methacryloxypropyltrimethoxysilane;

DOW CORNING® Z-2306 SILANE Isobutyltrimethoxysilane (IBTMS);

DOW CORNING® Z-6341SILANE n-octyltriethoxysilane (nOTE);

Diallyl Maleate (DAM) available from Bimax Inc. of Glen Rock, Pa.;

Allyl methacrylate (AMA) available from BASF Corporation of Florham Park, N.J.

Butylated Hydroxy Toluene (BHT) available from Sigma Aldrich of Milwaukee, Wis.;

Magnesium oxide (MAGOX SUPER PREMIUM); available from Premier Magnesia, W. Conshohocken, Pa. 19428 USA;

DAW-45; aluminum oxide filler commercially available from Denka;

AL-43-ME; aluminum oxide filler commercially available from Showo-Denko;

CB-A20S; aluminum oxide filler commercially available from Showo-Denko;

Varox® DCBP-50 Paste; available from R T Vanderbilt Co., Norwalk Conn. 06856 USA;

Perkadox L-50-PS; a product of Azko Nobel Polymer LLC, Chicago Ill. USA;

TAIC; triallylisocyanurate from Sigma-Aldrich Corp. St. Louis, Mo., USA;

TYZOR TNBT; available from Dorf Ketal Speciality Catalysts, LLC, 3727 Greenbriar Dr., Stafford, Tex. 77477 USA;

TINOPAL OB, Optical brightener from BASF Corporation 100 Campus Drive Florham Park, N.J. 07932. USA;

DOW CORNING® TC 1-4173 is a 1-part platinum addition-cured thermally conductive adhesive.

II. Impact of Isomer Reducing Agent on Clustered Functional Polyorganosiloxane

A. Variation in Amount of Added Isomer Reducing Agent on Generation of T(Oz) and D(Oz) Units

In a dry 3-neck flask, 100 g DOW CORNING® SFD-119 (dimethylvinyl-terminated dimethyl siloxane), 6.2 g cyclic methylhydrogensiloxane, 14 g allyl methacrylate (AMA), 0.2 g butylated hydroxytoluene (BHT) and varying amounts of an isomer reducing agent (either OFS-1579, available from Dow Corning Corporation of Midland, Mich., or DBAP (2,6-Di-tert-butyl-4-(dimethylaminomethyl)phenol) were added and mixed under a nitrogen blanket. 0.12 g of a platinum catalyst (DOW CORNING® 2-0707) was added and the mixture was mixed for an additional 5 minutes. The mixture was then heated to 60° C. for 1 hour. The reaction was monitored by the reduction in the SiH peak at 2173 cm⁻¹ by IR spectroscopy. The mixture was cooled to room temperature and diallyl maleate (DAM) was added. The reaction mixture was analyzed by ²⁹Si NMR for the presence of T(Oz) and D(Oz) units. The results are summarized in Tables 1 and 2 below and indicate that the introduction of at least 100 ppm of an isomer reducing agent in the formulation (either OFS-1579 or DBAP) reduced the level of T(Oz) and D(Oz) units by at least 10%, which corresponds to at least a 10% reduction in the beta-addition of SiH groups of the methylhydrogensiloxane to the allyl methacrylate.

TABLE 1 OFS-1579 (ppm) 0 100 200 500 1000 T (Oz) 0.46 0.39 0.43 0.29 0.27 D (Oz) 1.81 1.42 1.38 1.49 1.36 % Decrease in Isomer 0 20.3 20.3 21.6 28.2

TABLE 2 DBAP (ppm) 0 100 200 500 1000 T (Oz) 0.46 0.34 0.37 0.16 0.27 D (Oz) 1.81 1.68 1.65 1.59 1.6 % Decrease in Isomer 0 11.0 11.0 22.9 17.6

B. Viscosity Comparison of Samples with and without Isomer Reducing Agent (Samples 1 and 2)

In a 10 liter Turello mixer, 5000 g of DOW CORNING® SFD117, 196.34 g of cyclic methylhydrogensiloxane, 467.76 g of AMA and 1.13 g of BHT were added and mixed for 15 minutes. 5.45 g of platinum catalyst was then added and the mixture was mixed for an additional 15 minutes at room temperature. The mixture was heated to 80° C. for 1 hour, wherein samples were evaluated by IR for the disappearance of SiH signal. At 1 hour the mixture was cooled to less than 45° C. wherein 11.33 g of DAM was added. The vacuum was set to 55 mm Hg and the temperature was increased to 80° C. and the mixture was stripped for 30 minutes. The resultant composition (Sample 1) was cooled to less than 30° C. before packaging.

In a 10 liter Turello mixer, 5000 g of DOW CORNING® SFD117, 196.34 g of cyclic methylhydrogensiloxane, 467.76 g of AMA, 1.13 g of BHT and 1.13 g of OFS-1579 were added and mixed for 15 minutes. 5.45 g of platinum catalyst was added and the mixture was mixed for an additional 15 minutes at room temperature. The mixture was heated to 80° C. for 1 hour, wherein samples were evaluated by IR for the disappearance of SiH signal. At 1 hour the mixture was cooled to less than 45° C. wherein 11.33 g of DAM was added. The vacuum was set to 55 mm Hg and the temperature was increased to 80° C. and the mixture was stripped for 30 minutes. The resultant composition (Sample 2) was cooled to less than 30° C. before packaging.

Samples 1 and 2 were measured for viscosity (in centipoises (cps)) using a Brookfield LVF viscometer at 3 revolutions per minute using a #3 spindle. The results, as shown in Table 3, indicate that the introduction of the isomer reducing agent (Sample 2) provided a relatively stable viscosity over a 194 day period, while the viscosity of the corresponding example (Sample 1) without the isomer reducing agent increased to almost double the viscosity after 127 days and to the point of gellation after 194 days.

TABLE 3 Days of aging Initial 127 194 Sample 2 9200 9600 9600 Sample 1 6800 11600 Gelled III. Impact of Isomer Reducing Agent on a Silicone Reactive Diluent (Samples 1 and 2)

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 g of BHT, and 318.69 g of AMA were loaded. The mixture was inserted using 2% oxygen in nitrogen atmosphere and stirred for 10 minutes, at which point 6.64 g of a platinum catalyst was added. The mixture was stirred for 10 additional minutes before setting the temperature at 50° C. The temperature was held for 30 minutes at 50° C. before adding 9.96 g of DAM. The mixture was stirred for 10 additional minutes. The temperature was held for 30 minutes at 50° C. at a vacuum of 75 Torr. The resultant composition (Sample 1) was cooled to less than 30° C. before packaging.

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 g of BHT, 318.69 g of AMA, and 1.3 g of OFS-1579 isomer reducing agent were loaded. The mixture was inserted using 2% oxygen in nitrogen atmosphere and stirred for 10 minutes, at which point 6.64 g of a platinum catalyst was added. The mixture was stirred for 10 additional minutes before setting the temperature at 50° C. The temperature was held for 30 minutes at 50° C. before adding 9.96 g of DAM. The mixture was then stirred for 10 additional minutes. The temperature was held for 30 minutes at 50° C. at a vacuum of 75 Torr. The resultant composition (Sample 2) was cooled to less than 30° before packaging.

Samples 1 and 2 were measured for viscosity (in centipoises (cps)) using a Brookfield LVF viscometer at 60 revolutions per minute using a #3 spindle. The results, as shown in Table 3, indicate that the introduction of the isomer reducing agent (Sample 2) provided a relatively stable viscosity over a 90 days period, while the viscosity of the corresponding example (Sample 1) without the isomer reducing agent increased to almost double the viscosity after 90 days.

TABLE 4 Days of aging Initial 91 Sample 1 240 cp 400 cp Sample 2 250 cp 250 cp IV. Preparation of Thermally Conductive Thermal Radical Cure Silicone Adhesive

A. Preparation of Methacrylate Clustered Silicone Polymers without a Masterbatch and with an Isomer Reducing Agent (MCP-2).

In a 50 liter Turello mixer, 6 kg of DOW CORNING® SFD120 polymer, 176.92 g of cyclic methylhydrogensiloxane, and 274.74 g of chain extender Q2-50575 were loaded. The mixture was inserted using 2% oxygen in nitrogen atmosphere and stirred for 10 minutes. A homogenized mixture included 1.08 g of BHT, 537.58 g of AMA, and 1.08 g of OFS-1579 isomer reducing agent was introduced to the mixture. The resultant mixture was stirred for an additional 10 minutes at room temperature, at which point 8.03 g of a platinum catalyst was added. The mixture was stirred for 10 additional minutes before setting the temperature at 80° C. The temperature was held for 30 minutes at 80° C. before cooling to lower than 50° C. and adding 12.05 g of DAM. The mixture was stirred for 10 additional minutes before setting the temperature at 80° C. The temperature was held for 30 minutes at 80° C. at a vacuum of 75 Torr. The mixture was then cooled to less than 35° C. The resultant polymer is hereinafter referred to as MCP-2.

B. Synthesis of Silicone Reactive Diluent (SRD-1)

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 g of BHT, 318.69 g of AMA, and 1.3 g of OFS-1579 isomer reducing agent were loaded. The mixture was inserted using 2% oxygen in nitrogen atmosphere and stirred for 10 minutes, at which point 6.64 g of a platinum catalyst was added. The mixture was stirred for 10 additional minutes before setting the temperature at 50° C. The temperature was held for 30 minutes at 50° C. before adding 9.96 g of DAM. The mixture was stirred for 10 additional minutes. The temperature was held for 30 minutes at 50° C. at a vacuum of 75 Torr. The mixture was then cooled to less than 35° C. The resultant polymer is hereinafter referred to as SRD-1.

C. Preparation of Thermally Conductive Adhesives (TCA) Using Premade Silicone Polymers

In a 1 quart Gallon Baker Perkin mixer, 75.27 g of MCP-2, 128.53 g of SRD-1, 461.06 g of Al-43-ME (Al2O3 filler), and 19.52 g of DOW CORNING® Z-6341 (filler treat agent) were loaded. The mixture was stirred for 30 minutes before setting the temperature at 90° C. The temperature was held for 30 minutes at 90° C. with a vacuum before cooling to lower than 50° C. 691.58 g of DAW-45 (Al₂O₃ filler) and 3.45 g of MgO₂ were added. The mixture (M-1) was mixed for 30 minutes at room temperature (<30° C.) with a vacuum. Adhesive compositions were prepared by further adding promoter packages and radical initiators as provided in Table 5 below. Z-6030 was loaded in 2 steps to reach the total amount described in Table 4. In between the 2-step loading, there was 30 minutes of mixing at room temperature.

In a 1 quart Gallon Baker Perkin mixer, 166.12 g of MCP-2, 1058.47 g of Al-43-ME (Al₂O₃ filler), 105.85 g of DAW-45 (Al₂O₃ filler) and 38.26 g of DOW CORNING® Z-6341 (filler treat agent) were loaded. During the loading, Al-43-ME and Z-6341 were loaded in 3 steps to reach the total amount described above. In between the 3-step loadings, there was 2-5 minutes of mixing at room temperature to mesh in the fillers. After all the components (described above) added in the mixer, the mixture (M-2) was stirred for 20 minutes before setting the temperature at 90° C. The temperature was held for 30 minutes at 90° C. with a vacuum. The mixture (M-2) was cooled to lower than 30° C. before packaging. 663.6 g of this mixture (M-2), 717.7 g of DAW-45 (Al₂O₃ filler), 3.88 g of MgO₂ and 150 g of SRD-1 were added in a 1 quart Gallon Baker Perkin mixer. The mixture (M-3) was mixed for 30 minutes at room temperature (<30° C.) with a vacuum. Adhesive compositions were prepared by further adding promoter packages and radical initiators as provided in Table 5 below.

D. Preparation of Thermally Conductive Adhesives (TCA) Using Premade Silicone Polymers and Pretreated Thermally Conductive Fillers

In a 100max dental cup, 14.5 g of a mixture of MCP-2 and SRD-1 was made at various weight ratios (60:40, 50:50, 40:60 and 35:65 respectively). 49.8 g of CB-A2OS (pretreated with Z-6341), 33.2 g of Al-43-ME (pretreated with Z-6341) and 0.5 g of MgO were added to this mixture. The mixture (M-4) was mixed at 2000 rpm for 15 seconds, and repeated mixing 2 more times with 10 minutes in between. Adhesive compositions were prepared by further adding promoter packages and radical initiators as provided in Table 5 below.

TABLE 5 Thermally conductive adhesive (TCA) formulation (unit in gram) M-1 1379.4 M-3 1519.9 M-4 98 Z-6030 Silane¹ 13.84 7.69 0.5 Z-6040 0.5 TAIC 0.5 Z-2306 Silane² 2.07 2.3 TYZOR TNBT³ 0.69 0.77 Allyl Methacrylate 0.41 0.46 Varox DCBP-50 Paste 6.9 7.69 0.5 Butylated 0.03 Hydroxytoluene V. Evaluation of Physical Properties of Adhesive Composition

Viscosity Measurement on TCA Formulations:

In the following examples, a Brooksfield cone and plane viscometer (DV-II, spindle #52, speed 2 rpm) and a Brooksfield RVF viscometer (spindle #7, speed 2 rpm (low shear) and 20 rpm (high shear)) were utilized to determine the viscosity of the various thermally conductive adhesive formulations.

Sample preparation on Alclad™ Panels:

1″×3″ Al Alclad® Panels (available from Alcoa) were cleaned with acetone (3 samples prepared). Bondlines were established using Spheriglass spacer beads (Potters Industries Inc. 350 North Baker Drive, Canby, Oreg. 97013-0607) appropriate with the application (i.e, 23 mil).

Next, the adhesives were applied to Alclad™ aluminum substrates. Two ⅜″ binder clip were used with spacer methods to secure substrates during cure. The Cure condition was 30 minutes at 85° C. One half of the samples were evaluated at room temperature and aged, while the remaining samples were placed in 150° C. oven for 3 days.

Testing was carried out on Instron 5566 tensiometer at 2 inches per minute (Instron Worldwide Headquarters, 825 University Ave., Norwood, Mass. 02062-2643). The lap shear adhesive properties of the coated substrates were evaluated for peak stress, in pounds per square inch (PSI), with the results summarized in Table 6-8 below.

Preparation of Thermally Conductive Adhesive (TCA) Formulation Samples for Physical Test and Thermal Conductivity:

The TCA material in dental cup was removed from a freezer and allowed to warm up to near room temperature for at least one hour. The cup of material was then placed in chamber and full vacuum was pulled for 15 minutes. Approximately 56-58 g of the material was then poured carefully into 4″×4″×0.075″ chase to try and minimize introduction of air into the material. The chase was used along with Teflon sheets on each side to help with the release of material and to produce smooth surfaces, and two backing plates were used to help shape the slab. The chase, between the two backing plates was then placed into a Dake hot press at 85° C. and 10 tons of force was applied for 30 minutes.

After cure, material was removed from the hot press and allowed to cool to room temperature. Then, the slab of material was trimmed around the edges and removed from the chase. From this slab, using a “dogbone” shaped cutter and press, 5 samples were cut for tensile and elongation testing. Three (labeled RT samples) were tested 24 hours after cure. The remaining two samples were exposed to 150° C. for 3 days before testing and were labeled TRT samples.

The Instron T2000 tensometer was used to perform the physical testing, with the test program titled “Standard Tensile Test”. The leftovers from the slab (pieces that were not pulled) were utilized for Durometer and thermal conductivity measurement. The stack of three pieces reached 6 mm thickness (ref as the stack). For Shore A Durometer, 5 readings were taken. For HotDisk thermal tester (TPS 2500S Therm Test Inc), two stacks were placed on the top and bottom of thermal test probe. The measurement was taken with the setting as output powder 0.25 w and time measure 10 s.

TABLE 6 TCA from M-4 in Table 5 with various ration between MCP-2 and SRD-1 MCP-2:SRD-1 Cure condition Viscosity (before cure) Elongation 60/40 85° C. for 30 mins 340e3 cp 25-27% 50/50 250e3 cp 26-27% 40/60 170e3 cp 18--21% 35/65 150e3 cp 19-22%

As Table 6 confirms, the introduction of the silicone reactive diluent to the adhesive formulations resulted in a significant reduction in the viscosity while retaining the low temperature cure profile and slightly reduced elongation.

TABLE 7 TCA in Table 5 viscosity (before cure) Viscosity at Viscosity at TCA from low shear high shear M-1 100e3 cp 62e3 cp M-3 140e3 cp 70e3 cp Dow Corning ® 230e3 cp 63e3 cp TC 1-4173

As Table 7 confirms, the adhesive compositions (Table 5 Adhesives) according to the present invention exhibited similar viscosity at high shear that were achieved by compositions of the invention, relative to hydrosilylation cured compositions containing similar filler contents and loadings. The viscosity at low shear was lower than TC 1-4173.

TABLE 8 Properties after cure. TCA from M-3 in Dow Corning ® TC Table 5 1-4173 Cure condition 85° C. for 30 mins 150° C. for 30 mins Thermal conductivity 1.75 1.81 (W/mK) Shore A Durometer 87 92 Elongation, % 22 31.7 Tensile Strength, psi 655 714 Lap shear to Alclad ™ Al, psi 524 579 percentage cohesive failure 90% 100% after lap shear pull

As Table 8 confirms, the adhesive composition (Table 5 Adhesives) according to the present invention exhibited >1.5 W/mK thermal conductivity, adequate physical properties in terms of Durometer hardness, tensile strength, elongation, and lap shear on Alclad™ Al substrates. In addition, the adhesive composition (Table 5 Adhesives) according to the present invention cured at lower temperatures (actual cure condition or bond line cure condition) than platinum catalyzed addition chemistry adhesive systems. The introduction of silicone reactive diluents to the adhesive formulation retained the cure profile at low temperature (85° C. for 30 minutes).

The instant disclosure has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the instant disclosure are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the instant disclosure may be practiced otherwise than as specifically described. 

The invention claimed is:
 1. A method for forming a thermally conductive thermal radical cure silicone composition comprising (I) a clustered functional polyorganopolysiloxane; (II) a silicone reactive diluent; (III) a filler comprising a thermally conductive filler, (III′) a filler treating agent, and (IV) a radical initiator, the method comprising: (A) providing a clustered functional polyorganosiloxane (I) that comprises a reaction product of a reaction of: a) a polyorganosiloxane having an average, per molecule, of at least 2 aliphatically unsaturated organic groups, b) a polyorganohydrogensiloxane having an average, per molecule, of 4 to 15 silicon atoms and at least 4 silicon bonded hydrogen atoms per aliphatically unsaturated organic group in component a), c) a reactive species having, per molecule at least one aliphatically unsaturated organic group and one or more curable groups selected from acrylate groups and methacrylate groups, and in the presence of d) a hydrosilylation catalyst and e) an isomer reducing agent, wherein the isomer reducing agent is present in an amount based on the total weight of the clustered functional polyorganosiloxane (I) to produce at least a 10% reduction in beta-addition of SiH groups to the polyorganosiloxane to the aliphatically unsaturated group of the reactive species as compared to a clustered functional polyorganosiloxane formed in the absence of the isomer reducing agent; (B) forming a first mixture by mixing the filler (III) comprising the thermally conductive filler, the filler treating agent (III′), and at least one of the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I); (C) heating the first mixture to a temperature from 50° C. to 110° C. to treat the thermally conductive filler (III) with the filler treating agent (III′) (D) after heating in step (C), introducing the silicone reactive diluent (II), the clustered functional polyorganosiloxane (I), or neither to the first mixture as needed to obtain a final mixture that comprises both the silicone reactive diluent (II) and the clustered functional polyorganosiloxane (I); and then (E) cooling the final mixture to 30° C. or less and then blending a radical initiator (IV) with the final mixture to form a thermally conductive thermal radical cure silicone composition.
 2. The method according to claim 1 further comprising: (F) blending at least one additional component with the final mixture prior to Step (E), the at least one additional component selected from the group consisting of (III) an additional amount of filler comprising the thermally conductive filler, (III′) an additional amount of filler treating agent, (V) a moisture cure initiator, (VI) a crosslinker, (VII) a moisture cure polymer, (VIII) a solvent, (IX) an adhesion promoter, (X) a colorant, (XI) a reactive diluent, (XII) a corrosion inhibitor, (XIII) a polymerization inhibitor, (XIV) an acid acceptor, and any combination thereof, wherein, after performing Step (F), the final mixture to be used in Step (E) comprises the at least one additional component.
 3. The method as set forth in claim 2, wherein the (VI) crosslinker and the moisture cure polymer (VII) are both present in the thermally conductive thermal radical cure silicone composition and wherein the amount of the crosslinker (VI) comprises from 0.001 to 50 weight percent of the total weight of moisture cure polymer (VII) and wherein the amount of the moisture cure polymer (VII) comprises from 0.1 to 5 weight percent of the total weight of thermally conductive thermal radical cure silicone composition.
 4. The method as set forth in claim 2, wherein the moisture cure polymer (VII) comprises an organopolysiloxane polymer of the formula: (OR⁷)_(3-z)R⁶ _(z)Si-Q-(R²⁵ ₂SiO_(2/2))_(y)-Q-SiR⁶ _(z)(OR⁷)_(3-z), wherein each R²⁵ is independently a monovalent hydrocarbon group having 1 to 6 carbon atoms, each R⁶ independently is a monovalent hydrocarbon group having 1 to 6 carbon atoms, each R7 independently is selected from the group consisting of a alkyl group and alkoxyalkyl group, Q is a divalent linking group, the subscript z has a value of 0, 1 or 2, and the subscript y has a value of 60 to
 1000. 5. The method according to claim 1, wherein the silicone reactive diluent (II) comprises a reaction product of a reaction of: a) a polyorganohydrogensiloxane having an average of 10 to 200 silicon atoms per molecule, and b) a second reactive species having, per molecule, at least 1 aliphatically unsaturated organic group and 1 or more curable groups, in the presence of c) a second isomer reducing agent and d) a second hydrosilylation catalyst and e) inhibitor for the second hydrosilylation catalyst.
 6. The method according to claim 1, wherein the silicone reactive diluent (II) comprises a reaction product of a reaction of: a) a siloxane compound according to the formula:

wherein: R is a monovalent hydrocarbon having 1 to 6 carbon atoms, R′ is a divalent hydrocarbon having 3 to 12 carbon atoms, R″ is H or CH₃, and the subscripts m and n independently have a value from 1 to 10, and b) a second polyorganosiloxane having an average, per molecule, of at least 2 aliphatically unsaturated organic groups, in the presence of c) a second hydrosilylation catalyst and d) an inhibitor for the second hydrosilylation catalyst.
 7. The method according to claim 1, wherein the silicone reactive diluent (II) comprises from 20 to 90 weight percent of a total combined weight of the clustered functional polyorganosiloxane (I) and the silicone reactive diluent (II) in the thermally conductive thermal radical cure silicone composition.
 8. The method according to claim 1, wherein the thermally conductive filler comprises from 30 to 80 volume percent of the total volume of the thermally conductive thermal radical cure silicone composition.
 9. The method according to claim 1, wherein the clustered functional polyorganosiloxane (I) comprises from 20 to 99.9 weight percent of a total combined weight of the clustered functional polyorganosiloxane (I) and the silicone reactive diluent (II) in the thermally conductive thermal radical cure silicone composition. 